I and a friend of mine run another SMF forum for our Minecraft server, and we've been making use of
Stop Forum Spam's SMF plugin for quite a while now.
We haven't had any spammers get through our registration since we started that, and as far as I'm aware it's only blocked one legitimate registration (which was easy enough to let through manually.)
I know there's more issues with that on the wiki, but they have been getting to the forum lately too. And really, anything to hinder them is good, right?