At IndieWebCamp 2012 a bunch of participants noted that there are several building blocks we need in order to advance the indieweb beyond just being a collection of hyperlinked independent websites. One of those is the notion of Indie autosuggest, in particular, for typing/picking a person, e.g. using their name or alias (@-name or otherwise).
There are plenty of documented design patterns around the web for single line, static-content inputs (e.g. tag inputs, email To/CC/BCC), but hardly anything for multi-line, dynamic-content UIs where autosuggest is context-sensitive.
Examples from silos on their websites:
Facebook on facebook.com in their search bar at the top has excellent autosuggestion of names of people you are connected to, pages you've "liked", and even people you *may* know (i.e. 2nd degree).
Twitter on Twitter.com in their Compose Tweet Box:
GooglePlus on plus.google.com in the "share what's new…" box (if prefixed by @ or +), or bare in the to: or top search boxes will autosuggest,
Instagram in its app has autosuggest in its image description box for both users and hashtags:
Examples specific to a particular platform.
iOS Tweet Sheet
The iOS built in Tweet Sheet UI:
Twitter iOS app
The iOS Native Official Twitter App:
Lack of consistency
In conclusion, there is almost no consistency between UIs across platforms or even between platforms.
Common denominators (add more as they emerge):
sessions both discussed indie autosuggest a lot, and resulted in some code demonstrated as part of the day 2: