Spam Wait is a Movable Type hack cum plugin that forces your visitors to wait for a set period of time before being allowed to post comments. A decidedly smart move to avoid comment spamming by spam bots. The idea behind it? Human users would spend some time to read your entries/articles first. Spam bots wouldn't.
I won't install this, yet, but it is a smart idea. MT-Blacklist has been very good at blocking comment spammers and only 2 have filtered past it since I've installed it. Besides, judging from the behavior of past comment spammer activity, the majority of spammers at this site are human spammers, not bots. And now that my PageRank has dropped from 6 to 5, I'm pretty sure I'd see a sudden drop in comment spam activity here. Sort of a mixed blessing, that.