spamers usually have long email. You can check the length of the post and trow an error if possible.
I have deleted few of them in the last few days.
I've come across a couple of plugins for vbulletin, but I can see them slowing down page load times. A simple Geo IP check would be really fast and would only need to block access to the user registration page
Not that I can recallBtw Michele, have you had the ever famous polmki signing up here yet?