Being a fairly obscure blog, I don't get a heck of a lot of comment spam. But I've heard some blog authors going out of their mind deleting ads from comments. Almost as bad are inane posts like "that's because your a retard" that you find on some really old post. (Thank you Verizon customer 18.104.22.168). Crafty solutions to comment spam are cropping up daily now.
Blessed are the spam-blockers. I mean it. I love these people who are working on ways to block spam to help our lives become more signal and less noise. they are the warrior-angels of the information age.
I've previously mentioned POPFile for email filtering. It's great. A little work to set up, and it runs on your machine all the time, but it is worth it to me to not have to deal nearly at all with spam at home. However, spam on your blog comments is a little more complicated, and can be tougher to deal with. Here are some solutions.
MT Blacklist appears to be a great one-stop solution for filtering comment spam. It's free and requires no modification to your Moveable Type files. Administration happens through a web interface. This looks like the closest thing to a holy grail of blog spam solutions.
Close Comments Script allows you to shut comments off on old posts. This reduces the stupid comments people make when they wander in via search engine. You choose how long before comments are turned off. I'd probably go for 60 days. (Link via Ten Reasons Why -- look for where it mentions the "close comment script.")
Actually closing all comments off. This is a radical commentectomy. I'd rather not do this. The comments are most of the fun. And I certainly haven't gotten enough spam to warrant it.
Making users register (authentication) before commenting. Nah. Pain in the neck.
Just relax and enjoy the spam. Not an option. Spam begets spam. When spammers see your URL in their referrer logs, it's like sharks smelling blood. You have to delete all your comments spam.