These people are smart... what ever happens if they're determined enough they'll just keep coming back with new accounts. I think that there should be some kind of special check or some type of good question before an account is made... I think that's probably the best chance. Yes, they'll most likely get past it, but in my experiences it can get had to stop a determined spammer. Unless there's a way for the spam stuff to get deleted by the computer if it's caught or something I'm not sure there's anything that can stop them... only stuff to slow them down. They don't care if they get banned, again, they'll keep coming if they want to. And if post approval is put in it might pile up to be a lot of work for the mods. I mean they're the ones that approve this stuff, correct?
So ya just a thought.
Edit: The humans are more of a problem than the bots. Bots are just a computer... there's almost always a way to stop a computer. A human though.... not so much.