Re: Flooding user accounts
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.