There have been many discussions on this topic (most started by me) about finding a solution to use akismet or something to stop the registration spam in bbPress. While there are no solutions availabe right now, there are several TRAC tickets at http://trac.bbpress.org about this issue for future development.
In the meantime, you can either disable the registration, install the MemberList plugin from Ardentfrost (gives easy admin interface to delete users quickly) or maybe search forums for another solution. I know that I use the MemberList plugin to delete users quickly, but also delete all the BOZO users as well.
I would agree that the registration spam issue will have to be dealt this soon as a standard release feature.
Trent
bbPress should already be filtering new registrations thorugh Akismet; if you have Akismet set up, it should mark as “bozo” any new registrations.
There may, of course, be bugs particularly if you’re loading both bbPress and WordPress at the same time.
FWIW I’ve kept bb stand alone for simplicity but I’m still getting a lot of registration spam that misses Akismet, so what are the plans for an Akismet UI in the admin panel? It’s all very black box at the moment, which is probably what’s causing a lot of these questions.
I don’t have many that make it through Akismet for not being marked as BOZO, just the fact that BOZO or not they are pulled over to WordPress through the integration plugin. Soon enough we will fix this!
Trent