I've been using SpamAssassin for a week or so, ever since the WELL switched it on on their mail-servers. It is fantastic. I get in excess of 1,000 emails every day, and more than half are spam, and SpamAssassin just nails 'em. I get one or two false-positives a day, tops, and only two or three false negs. It's made my life livable again.
But what do you do if you don't run your own mailserver? Well, if you're running OS X, you can install SpamAssassin locally and have it prune your mail on your own computer. Ben "Movable Type" Trott has written an excellent tutorial on running SpamAssassin under OS X.
(Thanks, Merlin!)
