If you run a blog, no doubt you've been hit with trackback or comment spam. These idiots should be shot. I run my sites on TypePad and SixApart seems to have it under control for us, but Moveable Type users are getting slammed.
A buddy of mine, Ryan Saghir, has written some code to help Moveable Type customers with the problem. I think his solution rocks. Check it out at: http://www.ryansaghir.com/archives/000117.html.