BuddyPress.org

@lairbear spam is an issue that is almost impossible to control, even the big proprietary social networks have a huge issue with spam – and they have alot of money to spend on controlling it. (I’m very popular with all of the really, really hot ladies on Facebook… lol)

In BuddyPress 1.6 their will be some anti-spam tools for the activity feed built-in that will hook into Akismet (http://akismet.com) to help control it, and while it has cut it down by alot on my test sites using it, nothing can beat manual HUMAN moderation. (Related ticket: https://buddypress.trac.wordpress.org/ticket/3660)

Theirs also afew plugins that add captchas to the registration page, to kick them out before their even in… oh, and this article is pretty comprehensive – http://wp.tutsplus.com/tutorials/security/best-practices-for-preventing-buddypress-spam-user-registrations/