I just installed an anti-spam filter for the comments on my site. It was written by James Seng, and uses a Bayesian network to detect probable spam -- just like many popular email filters. We'll see how it works. I don't get a lot of spam here, so it may take some time to train it. Meanwhile, I won't have it actually filter anything, so no comments will be lost.
No, I cannot resist adding artificial intelligence to everything, whenever possible.