So after only one evening of spam training, it already is doing a respectable job. Last night out of 12 emails I had one false negative and one false positive. I'm expecting the results will get better as it gets more data.

One confusing thing in my original post, I said "for those of us running Windows." This program is actually written in straight Perl, and should therefore run on anything that runs Perl. I just mentioned Windows because there didn't look to be many solutions for Windows users, short of switching POP clients. The thing I like about this is that it works with your exisitng POP clients, and flags the messages before your POP client downloads them (for easy filtering by the POP client.) It's got a really slick HTTP-based configuration interface as well.

The things keeping me from going with one of these spam programs before were the need to switch clents and the difficulty of configuring them, but this program really has the right approach. Y'all should check it out if you're sick of spam. Oh yeah, it's free (but the author accepts donations.)