I read on the phpBB forums that the Q&A captcha is a lot more effective than the obfuscated image captcha, so I've enabled that. Let me know if any of the questions are too difficult or not-obvious.

Other admins: feel free to add some more questions, I've only got about 3 right now. It's under the "General" tab, "Spambot Counter-measures" section. Make sure the answers are simple, one or two words at max, but not just like "2+2=?"

Hopefully this helps with the spam.