All I know is that it has its limits. This
board for example runs vB and they have trouble basically each and every day. They constantly have about 400 logged in and often it either doesn't count posts, or doesn't track the threads properly or gives other bunch of crap
They have (I think) two machines dedicated to the forum, one for the db, and one for the forum itself... you should really go with UBB if you want a funtioning BBS running.
