I don’t think this feature is listed anywhere, which isn’t surprising because it’s one of those thousand small things that you just can’t get into detail about in a sales pitch, but:
#Did you know?..
When you start writing someone’s @username in a Discourse thread, good-guy Discourse will start out by suggesting the people involved in that thread. Ammagerrd I love it!
I don’t use social networks much so maybe this is commonplace. In any case, I’ve never seen such a polish type of feature put to better use.