One thing that I noticed was missing from the /users/ API was an ability to see what other Stack Exchange sites the user is associated with (what's usually available from the "accounts" tab of the user details screen.) Are there any plans to incorporate this functionality into the API?
Please see this answer for some more details.
The short of it is, there isn't really a good place to shove this kind of data yet. Especially if you're planning for the Count(Sites) > 5 case, which we are.
StackAuth implements this feature now.
For the record: this has been completed in the meantime via the StackAuth routes. The official versioned API routes documentation/help link is going to change soon, but should always be reachable via the respective FAQ and Stack Apps question number 1 (API Documentation and Help).
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