After last nights troll attack I got to thinking. This guy posted ~300 times in 3 hours, an average of 100 posts an hour. If there was a time limit that one would have to wait, say 1 - 2 minutes, between posts the amount the troll posted could have been reduced. ~30-60 an hour, or 90 - 180 total.
A one to two minute wait between posts shouldn't cause too much problems, this is usually the time a normal person would take between posts plus it adds a form of security against spamming/trolls.
EDIT: Another idea, would there be a way to test if the post you are submitting is identical to a previous post you've recently submitted?