Site deaths are when sites go offline, taking their content and permalinks with them, and breaking the web accordingly. Site deaths are one of the big reasons why you should own your own identity and content on the web.
This is a chronology of content hosting sites that have died, removing millions (billions?) of permalinks from the web. This is specifically for content hosting sites which permitted end-user posting. Not random sites nor pure "app" sites where there's no loss of user data. If a game site goes down and takes down play history/scores, or if Gmail went away those would both represent loss of user data (though no public permalinks).
The tendency for big companies to shut down a service and delete all your things has now even been satirised by XKCD. Andy Baio talks through one example from creation, to growth, acquisition, disillusionment, neglect, and shutdown.
This is a partial list, please add more, e.g. from other sources like:
Expected/announced site deaths. Check them upon announced shutdown date.
- If site shutdown is confirmed, move to #Past by year.
- If site is still up as of shutdown date, move to #Any_Day_Now
- 2014-06-01 Ubuntu One cloud sync service run by Canonical, makers of Ubuntu, to be discontinued.
- ". . . user content will remain available for download until 31 July, at which time it will be deleted."
- 2014-06-25 Springpad "will be shutting down."
- 2014-07-01 Readmill "app will no longer be available ... All of your books, reading data and account information will be permanently deleted. User information will not be archived, shared or saved in any way.".
Export data includes books, followers, followings, readings, highlights, reviews, comments and likes on your highlights and reviews, and highlights you liked.
- ???? Readmill profiles being lost, including followers/followings lists, readings, highlights, reviews, comments, likes, comments and likes on your highlights and reviews, and highlights liked
- ???? purchased ebooks lost
- 2014-08-01: Svpply will be sunset by eBay. Export of link data added to the site is available from users' account settings. In response, the founder launched a Kickstarter campaign to build a new version of the site, called Very Goods.
- 2014-09-01: mlkshk.com image sharing site shutting down. 
MLKSHK isn’t our primary source of income and it’s certainly not our primary focus. Despite earning very little from the site we still have to answer tech support, deal with spam, fix minor issues, fix major issues, keep the servers updated, sort out billing issues, and worry about the months we get linked on Reddit. Sometimes the server and bandwidth bill are more than we took in for the month—this is scary.
- Data export:
Yes! You can either email email@example.com with your user name or click the link “Request Zip File Of All My Images” on your account settings page. It should take about a day to process your request if we don’t get inundated with requests.
- Will be working with Archive Team to have data stored there as well. 
- 2014-09-30 Orkut will shut down but it looks like they might not break the public archives.
- "We are preserving an archive of all public communities, which will be available online starting September 30, 2014. If you don't want your posts or name to be included in the community archive, you can remove Orkut permanently from your Google account." source
- 2017-04-30 Google and Facebook "might completely disappear"
Any Day Now
These sites are officially closed, but some functionality may still be working (e.g. logging in and viewing your activity).
- 2014-05-16 Loom cloud-based photo storage
- Announced being acquired by DropBox 2014-04-17.  
- No longer enrolling new users. Existing Loom users can continue to use our service until May 16, 2014
- 2014-05-31 site appears to still be up for existing users. - Tantek
- 2014-02-01 myOpenID officially closing on 2014-02-01, but appears to still be online.
This is an incomplete list. Please help by adding examples from these sources (in particular when user authored content was lost):
See also (and add one-line summaries to) the history page.
In reverse chronological order:
- 2014-06-17 Codespaces.com experienced a DDOS and an unauthorized person gained access to their EC2 control panel.
- From http://www.codespaces.com
. . . removed all EBS snapshots, S3 buckets, all AMI's, some EBS instances and several machine instances.
In summary, most of our data, backups, machine configurations and offsite backups were either partially or completely deleted.
Code Spaces will not be able to operate beyond this point, the cost of resolving this issue to date and the expected cost of refunding customers who have been left without the service they paid for will put Code Spaces in a irreversible position both financially and in terms of on going credibility.
As such at this point in time we have no alternative but to cease trading and concentrate on supporting our affected customers in exporting any remaining data they have left with us.
- 2014-06-15 Justin.tv no longer archiving live broadcasts and will be deleting all archived videos with two weeks notice.
- 2014-05-30 Editorially collaborative writing and editing platform
- Service will be shut down; did not get enough users to make it sustainable. Users have until shut down date to export their data. Archive will include a plain text file for every version of every document you have access to; it will also include comments, version notes, tags, activity, and other metadata about your documents. That metadata will be provided in the form of a YAML file. https://editorially.com/help
- 2014-06-24: Announced that Editorially has been acquired by Vox Media and they want to "release parts of the code via an open source license." Interestingly, "Absolutely no user data — no names, email addresses, documents, or any other user data — will be transferred to Vox Media."
- 2014-12-31: "Remaining data backups will be permanently deleted" (until then "users may request a backup of their data by emailing firstname.lastname@example.org" - http://editorially.com/ )
- 2014-03-15 Zootool.com "shutting down". Site already has goodbye message as of 2014-02-10. Email also sent to users with same message dated 2014-02-10.
- Deletion coming:
On March, 15th all data and images will be deleted forever.
- 150,000+ user profiles will be lost
- "millions of collected items" will be lost
- Amazing insight quote in shutdown notice:
Zootool made us realize that the general idea of running a central service is nothing we believe in any longer. Your data should belong to you and shouldn't be stored on our servers. You shouldn't have to rely on us or on any other service to keep your data secure and online.
- Data export promise:
You will have the chance to export your data over the next weeks. We offer export for bookmark files, which can be used to import your bookmarks in all common browsers and most other bookmark services. You can find the export in your Settings.
- 2014-02-14 Read only mode expected:
Starting by the end of this week we are going to switch Zootool into read-only mode. You will still be able to browse your collection, but you will not be able to add new bookmarks.
- 2014-03-06 Vizify gets bought by Yahoo! and will be "sunsetted" (oh, euphemisms!) on 2014-09-04.
- 2014-02-27 Donna by Incredible Labs (intelligent personal assistant app)
- Incredible Labs Acquired By Yahoo, Mobile Assistant App Donna To Be Shut Down.
- 2014-01-02 Ptch shut down. Ptch Joins Yahoo. Instructions provided for how to save user content.
- 2013-12-12 ClaimID "ceased operations" after "7 years, 6 months, and 20 days of service".
- 100,000s profiles / identities lost
- 2013-12-01 HipGeo travel journal app that allowed people to track their travels and location. Site replaced with a WordPress installation with one post and a default comment. All permalinks from Google search results for the brand broken . ??? profiles lost. Shutdown announcement: 
- 2013-11-05 Everpix photo content hosting silo announces shutdown, immediately goes "read-only", and says they will "email instructions to all Everpix users on how to download their photos". 
- 2013-11-05- Sold, a service to help people sell things, was acquired by Dropbox and shut down. **http://usesold.com/
- 2013-11-01 iGoogle shut down What's happening to iGoogle? The mobile version was retired on 2012-07-31.
- 2013-11-01 Dopplr discontinued (home page and ).
- 2013-09-28 Yahoo! Term Extraction API (citation needed)
- We are eliminating direct access to the Yahoo! Term Extraction API and as of September 28, will require developers to go through YQL. We encourage all existing users of the Term Extraction Legacy API to migrate to YQL requests by September 28. You can use the YQL forums for any questions you might have about migrating to YQL. If you are already using the Term Extraction API via YQL, you don’t need to take any action.
- 2013-09-19- .Net Magazine, a web industry magazine, merged with creative bloq
- how many URLs lost? apparently top 500 articles out of > 9000 were moved with proper redirects, working on moving others
- 2013-08-05 Yahoo! Astrid (task tracking service)
- 2013-09-28 Yahoo! Local API (citation needed)
- As part of this shutdown, all Yahoo! Local API documentation will also be removed from the Yahoo! Developer Network portal.
- 2013-08-21- Alice.com a grocery delivery service, shuts down. Launch article from 2009. http://news.cnet.com/8301-17939_109-10270643-2.html Announcement of Shutdown on YCombinator. https://news.ycombinator.com/item?id=6250893
- how many user accounts were lost?
- as any user content lost?
- were any public permalinks to user content lost?
- 2013-08-09 Google Latitude retired.
- 2013-08-09 Silent Circle Maryland-based encrypted private email provider preemptively shut down following suit of Lavabit. Two Providers of Secure E-Mail Shut Down, Silent Circle Preemptively Shuts Down Encrypted Email Service To Prevent NSA Spying
- 2013-08-08 Lavabit Texas-based encrypted private email provider shut down due to its affiliation with being whistleblower Edward Snowden's email provider since 2010. Lavabit's founder Ladar Levison decided to shut down the service after a cost benefit analysis on whether to shut down the service or become "complicit in crimes against the American people". Lavabit, email service Snowden reportedly used, abruptly shuts down
- 2013-07-24 Snapjoy shut down after being acquired by Dropbox. article
- 2013-07-08 Yahoo! Neighbors Beta (was local.yahoo.com/neighbors) shutdown.
- Unknown number of user questions & answers lost.
- 2013-06-12 Myspace.com User blogs after MySpace redesign. MySpace Punishes Its Few Remaining Friends By Vanishing Their Blogs
- 2013-04-30 Upcoming.org after being acquired by Yahoo
- 2013-04-30 Posterous.com Thanks from Posterous after being acquired by Twitter
- 2013-02-07 EveryBlock.com ultralocal news/information site shutdown with "zero warning". Farewell, neighbors
- ???? friends lists lost. 
- ???? discussion threads lost. (ibid)
- 2013-01-30 Yahoo! Voice Phone In and Phone Out feature shut down
- 2013-01-22 Mixel  - social network shut down. (Mixel has been acquired by Etsy)
- App removed from Apple's App store, network shutting down early September (2012-09).
- current Mixels can be shared, bulk export functionality on its way
- ???? user profiles lost
- 2012-12-24 Yahoo! Messenger Public Chat Rooms, Yahoo! Messenger Pingbox, Yahoo! Messenger interoperability with Microsoft Windows Live Messenger, shut down
- 2012-12-03 Twistory 
- Not accepting new users as of 2012-11-07
- Paying users were no longer be billed, and had "several months" to download a .csv of their data
- 2012-10-31 Batch.com photo sharing site shut down. article
- 2012-10-12 DailyBooth photo sharing site shut down. article
- 2012-09-02 picplz - last day to login and download photo archives.
- 2012-07-03 site already shut down
- 2013-08-02 domain not found
- 2012-07-20 KLIK - last day to login and download photo archives
- Going down with the Face.com API due to acquisition by Facebook.
- 2013-08-01 domain not found
- 2012-07-05? Plazes downloads.
- Export was available (for who knows how long) - "you can download and keep your Plazes history" (checked as of 2012-07-05)
- 2012-06-30 site officially shut down. See below.
- 2012-07-03 picplz has shut down.
- 2012-09-03 "Photo archives will be available until September 3, 2102" (ibid)
- picplz shut down planned 
- 2012-06-30 Plazes. 
- Export available (for who knows how long)
- 2012-06-30 Apple MobileMe Gallery, iDisk, iWeb downloads.
- 2012-06-30 Apple MobileMe Gallery, iDisk, iWeb,,email
- as of 2012-07-05 on http://www.me.com: "For a limited time, you can still move your account to iCloud, download your photos from Gallery, and download your files from iDisk."
- who knows how long you can still get your data.
- "Closed." screenshot(on Flickr).
- 2011-06-06 Apple Support Communities: What happens to iWeb when there's no Mobile Me?
- Note first comment: "FYI, Apple is deleting some topics pertaining to people voicing their opinions on iWeb and iDisk. Just be careful."
- 2012-05-30 Tabblo shutdown by HP. Was at http://tabblo.com
- ??? number of photos lost (Archive Team has "almost everything" and is posting them to Archive.org)
- ??? number of "tabblos" (collection of photos) lost
- ??? number of links to photos / tabblos broke
- 2012-01-31 All original Tabblo employees gone (from HP) as well as those they directly hired.
- 2007-03-23 HP acquired Tabblo.
- "five million pictures" (at time of acquisition)
- 2006-06 Tabblo launched. (ibid)
- 2012-05-01 Google Knol discontinued - was at knol.google.com
- 2012-10-01 Download your Knol - til 2012-10-01.
- ??? number of Google Knol pages lost
- ??? number of links to Google Knol pages broke
- 2008-07-23 Google Knol launched to the public.
- 2007-12 Google Knol private beta launch.(ibid)
- 2012-04-30 Google Wave shut down.,
- 2012-01-31 Google Wave went read-only.(ibid)
- ??? number of Google Waves lost
- ??? number of migrated Etherpads lost
- ??? number of links to Google Waves broke
- 2010-08-04 Shutdown implied: "We don’t plan to continue developing Wave as a standalone product, but we will maintain the site at least through the end of the year..."
- 2012-03-11 Gowalla shut down
- ??? number of user profiles lost
- ??? number of user check-in permalinks lost
- 2012-03-01 Google Friend Connect retired for all non-Blogger sites - was at www.google.com/friendconnect
- Export your community data - unknown how long it will be supported.
- limitation: "Export Community is limited to your site’s first 2000 members" (ibid)
- encouraged to transition to Google+: "create a Google+ page and place a Google+ badge on your site".
- 2008-05-12 Google Friend Connect launched.
- 2011-07-11 tr.im URL shortener failed.
- ??? number of tr.im short links lost
- ??? number of links to tr.im URLs broken (across the web, Twitter, etc.)
- 2009-12-31 redirecting promised thru this date (and worked)
- 2009-08-10 went read only. short link creation disabled.
- 2010-12-10 Brightkite shut down - was at brightkite.com
- ??? number of user profiles lost
- ??? number of user check-in permalinks lost
- 2010-09-30 Vox shut down - was at vox.com.
- 2010-09-15 Vox went read-only (ibid)
- ??? number of Vox blogs / posts lost.
- ??? number of migrated Pownce profiles lost.
- ??? links to Vox posts broke.
- 2010-06 icanhaz.com shut down URI shortener
- Had previously stopped accepting new URIs but continued to serve old ones
- 55437 short URIs lost
- 2010-05-15 Etherpad.com offline taken offline by Google. (including their own blog post of their transition: http://etherpad.com/ep/blog/posts/transition-update). Etherpad went read-only a month beforehand (2010-04-14).
- ??? number of Etherpad pages lost.
- ??? links to Etherpad pages broke.
- Migration advised: to Google Wave. "Current EtherPad users will also be getting invites to try Google Wave in the near future...", "EtherPad users got invites to use Wave..."
- 2010-05-14 Twine taken offline at twine.com by Evri and redirected to evri.com.
- 2010-03-11 Evry acquired Twine.
- ??? number of Twine pages lost.
- ??? links to Twine pages broke.
- 2008-10-21 Twine launched publicly
- 2009-12-31 Radio Userland service closing. 
- ?? number of blog posts lost
- ?? hosted comments and trackbacks lost
- 2009-12-29 Haloscan commenting service shut down.
- ??? number of comments lost
- ??? number of links to comments broken
- ??? number of blogs with embedded Haloscan commenting broken
- 2009-08-24 Microsoft Popfly went offline
- Warning given on 2009-07-16
- ??? number of user-created sites gone
- 2009-04 Dodgeball.com shut down by Google
- ??? number of Dodgeball profiles gone.
- ??? number of Dodgeball venues gone (user created)
- ??? number of venue reviews gone (user created)
- 2009-02-28(?) went read-only at "end of February"
- 2009-01-14 Shut down announced by Google
- Subsequent site: Google Latitude.
- 2009-02 Pownce.com went offline. Was previously scheduled to go offline 2008-12-15, but voluntary code patches/contributions from Tantek helped them to transition to public read-only access (to increase chance of archival of content) on that date for about 2 months.
- 2008-12-15 went read-only.
- ??? number of Pownce profiles gone.
- ??? links to Pownce posts broken.
- Migration Advised: import to Vox: "Six Apart is encouraging Pownce members to join its blog platform Vox".
- 2009-01-30 Ma.gnolia.com shutdown.. Ma.gnolia.com suffered catastrophic database corruption and lost all user data.
- 2008-03 Consumating.com shut down by CNET.
- ??? number of Consumating profiles/posts lost.
- ??? links to Consumating posts broken.
- 2008-10-31 AOL Hometown shutdown  by AOL.
- At least 14 million sites lost.  2002 stats estimate 14 million sites on Hometown that year.
- "Well it looks like AOL did it again. Another sneaky move. The Hometown pages all seem to have disappeared. [...] I only discovered this morning that AOL pulled the plug on Oct 31st, 2008." - taimantis.com, November 11th, 2008
- "Lots of information on AOL Hometown very important to people who put hard work into these efforts is being lost, possibly without notice." - David Dillard, "Meet the Googles" Visits the Grave Site of AOL Hometown to Ponder Its Past All to Short Life
- "I was surprised to find that AOL just shut down their homepage service on Oct. 31st. There were many great websites created through that service that simply no longer exist." - Dr. Jitters, November 12, 2008
- "I knew this was coming, I just didn't know the day. I tried, with the help of some great people, to get AOL to donate ficlets to a non-profit, with no luck. I asked them just to give it to me outright since I invented it and built it with the help of some spectacular developers and designers. All of this has gone nowhere. [...] I'm disappointed that AOL's turned its back on the community, although I guess I shouldn't be surprised." - Kevin Lawver, Ficlets Est Mort
- "A terrible thing happened recently. You might have missed it. AOL Hometown, which itself was actually a combination of a bunch of previously acquired websites, shut down. [...] It's all fine and good, those readers who sneer and say 'you get what you pay for' and 'ha ha, losers'. But the fact is, these people were brought online and given a place for themselves. Like a turkey drawn with a child's hand or a collection of snow globes collected from a life well-lived, these sites were hand-made, done by real people, with no agenda or business plan or knowledge, exactly, of how everything under the webservers worked. They were paying for their accounts, make no mistake – this was often provided to them as a tool combined with their AOL accounts. Some were absorbed from other companies as AOL purchased them. Some of these websites had existed for a decade. [...] We're talking about terabytes, terabytes of data, of hundreds of thousands of man-hours of work, crafted by people, an anthropological bonanza and a critical part of online history, wiped out because someone had to show that they were cutting costs this quarter." - Jason Scott, Eviction, or the Coming Datapocalypse 
- 2001 Desktop.com shutdown suddenly, without users being able to download their documents.
- ??? user profiles lost
- ??? user documents lost
- 2001 SixDegrees.com (wikipedia), one of the first social networking services
- 2000-07-02 PlanetAll shutdown by Amazon.
- 1.5 million user profiles lost including address books, calendars, buddy lists. (ibid)
- 2000-06-06 Amazon told users "PlanetAll.com will be going away"(ibid)
- 1998-08-04 Amazon bought PlanetAll 
- 1996-11 PlanetAll launched
- Wannadoo/orange personal sites
- Zooomr.com photo sharing / flickr competitor
- Why - other problems with using and depending on 3rd party sites
- Google Graveyard (on pinterest.com)