[peterverkooijen]

The BB forum is for the people who installed Buddypress to get into this newfangled social networking thing and then decide they need something more familiar looking.

To my eyes the discussion beneath an item from the activity stream looks the same as the discussion in a forum.

Group Blog with front-end posting and threaded comments via P2 will do everything you can do with a forum, but in a much more native WordPress/Buddypress way.