Well, one thing to keep in mind is that a lot of these "automated attacks" aren't automated; organizations are actually there to spam sites with whatever advertisement that anyone wants to pay for (for pennies on the dollar).
One thing I recommend people who're being plagued with such issues is to install my Stop Forum Spam modification over at UBBDev. Stop Forum Spam keeps a database of users who've been known spammers and tells you if they match (the mod does an automated IP based match on signup, if a match is found, they're denied the ability to register).
