I've been playing with SpamProbe. It's really cool. I can drop any spam mail into a folder, and it'll automatically figure out what phrases make it a spam. I primed it with some mailboxes I had laying around on the hard drive (like mails from my friend Ruth who always got stuck in my other spam filter for some reason or another). So far it's working well, with about 90% success, and no false positives. Woo hoo!!!