My software allows me to ask multiple questions at signup that varies. That did slow them down a bit, but I still get the little buggers taking the time to answer various questions during signup, which I routinely change, with email verification, even, lol. They take the time to do all of that, then post some idiotic looking post filled with spam and about that time I delete them.
I guess I need to see if the forum software can limit on geography, and cut asia, africa, south america out, lol, maybe that will help.