One huge thing I would like is from the user page, a list of recent posts. Yes, just like the Slashdot user page.
Wait, I think I just coined a new truism. We all know any app will eventually expand until it can do email. Maybe every forum app will eventually expand until it's reinvented Slashdot.
Ooh, and on the user page maybe forum participation stats. ie: This user has posted 72 times in Politics, 19 times in Flame On, and 0 in Flame Off. And while I'm at it, since it would only be a matter of adding one more term to the WHERE clause, whatever stats you compile board-wide (top posters, hot topics, etc.) you can also do them on a per-forum basis.
Okay, let me sum up:
1) On the user page, last X posts.
2) Whatever stats you decide to do board-wide, also do them on a per-forum basis.