I've got some time this evening, so I'm going through the process of setting up fetchmail, procmail, and spamassassin on my TiBook. (fetchmail and procmail come installed on OS X) I hate SPAM.

Update: It worked! I've actually disabled my main pop account in Mail, and I'm letting fetchmail do the work for me. For now Mail is still filtering mailing lists and stuff, but soon I'll get procmail to do that too, since procmail's rules are actually useful…