This won't be such "huge" addition but, it's really cool to have (if possible to implement)
So yeah, tagging someone, just like facebook's feature. Would be really nice to tag someone in a reply you want him to see instead of sending him a pm or blablabla ways to reach him.
It's not that much of a use, but when used, it's probably a nice one
For example #Martin. He get an instant message telling him you've been tagged in a thread/reply and by who.
Maybe you could just make a new button for it near the "My Messages" tab up there, that's up to you though, I ain't no programmer.
Agree/Disagree and why