I have the same problem! I have bp 1.0.3 and bbpress 1.0.1. There is deep integration as well, use bbpress-integration plugin.
As reboot now says: *everything* works except posting on the forum (only admin can post to the forum). No errors, after posting I am returned to the forum home page and nothing is posted!!!
It used to work fine, but after I upgraded wpmu to 2.8.1 and bp to 1.0.3, it stopped working