Spock has a nice post on the promise (and some fair detail) of Bayesian filtering engines in the war against Spam. It will cheer you up when you find out that the spammers may actually be in a relatively hopeless position against the newest filters like POPfile!
I would concur. My organization has recently adopted POPfile (and Outclass) with very good results. Even more interesting, I recommended POPfile to someone at church who was complaining about spam and he liked it so much he went out of his way to tell me how happy he was with it.
How 'bout that? A rare cheery morning here at We The Free...