I sometimes can't imagine why it took me so long to figure out how to do something. For example, our blogs have been spammed heavily. Spammers would post links to their (mostly porn) sites to improve their pagerank in Google. You'd never see it of course because we diligently keep cleaning up the comments. Banning IP addresses didn't work anymore, and closing the enties for comments seemed a bith harsh. Requiring users to log in, as explained here, is not an atractive option. Six Log: Comment Spam
I realized that we were loosing the battle when I was getting more than 10 comments per entry at an alarming rate of something like one every 5 seconds. That did it for me. I was going to stop these miscreants. Fortunatly, there is MT-Blacklist - A Movable Type Anti-spam Plugin
I should have done this ages ago. Read the Comment Spam Manifesto
This is a fight against the spammers we're going to win.
Update: even the porn sites themselves are unhappy with the comment spammers. Wired News: CyberQuest Disavows Porn Blogs