Spam is a issue on all four of my forums too, I had to disable the Contact us page.. and I always used image verification but that does not seem to stop. I wish there was a hack for Image verification for sending emails.. but I disabled the feature instead. I also STOPPED accepting new registrations from @hotmail.com and @yahoo.com addresses. Which made alot of people mad, but oh well. That drastic move cut down the spam by about 60%. I allow @gmail.com which they seem to be very good at preventing spam -- So far.
I have also been doing something a bit evil which has cut down some of my spam and has generated a couple of "haters" aka "spammers" that registered and wrote a few nasty posts... I'm gonna try to fight as dirty as possible.
I started collecting tech support email addresses for the various ISP's and government offices. I have been including them is various codes and posts in attempts for the spam bots to pick them up. I managed to piss off a couple of spammers, I guess one got smacked down by some gov office in Canada... He decided to register on my site and try to bad mouth me. Needless to say, he is no longer a issue. The other one threated to fly over to the US and kick my ass.. Guess where that email was redirect too...