Don't want to discourage You guys, but only one effective method to fight it is more secure automatic verification system. Spambots are automates (obviously), so fighting man-power against it is a no-go for a long-term.

On the other hand, most spammers doesn't write their bots, they just use ones from net. So, it's relatively easy to block them, as they're not so adaptable. PHPbb got many installable method for blocking dumb bots, unfortunately, I got no idea about vBulletin. I suppose it's up to Reggie (joys of non-community governed hosting for forum)... Was he pinged about this serious problem, already?