Over the years I've had very good results with Spam Assassin, but the server-wide version here on DreamHost isn't as sharp as I'd like. Part of this is that I don't get to tweak the rules, and that it doesn't do Bayesian filtering. But the following email really puzzled me:
That should have hit a number of Spam Assassin rules as best I understand. Also note that the Spam Assassin version is missing.