After a few weeks with bogofilter, I'm pleased with my setup (Use procmail and bogofilter with Mail.app). It's filtering out around 250 spam messages per day with a 95% threshold, a couple of false negatives (ham that should be spam), and a relatively large database of tokens:
pbpbook> bogoutil -d ~/.bogofilter/wordlist.db | wc -l
544,279It's the best of the various filters that I've used; it even gets some of the annoying stock tip emails that used to regularly slip past SpamBayes.