SpamAssassin 3.1.0 for Dreamhost. DH currently provides SpamAssassin 3.0.3 by default, though some people are saying DH's installation is quirky. This installation tutorial is long and complicated, but it's Dreamhost specific, and I got some good hints from it for using the default 3.0.3 installation.

SA had a problem with reading its own Bayes token files at first, but I moved them out of the way and let sa-learn make new ones, and it works now. Maybe this is one of the quirks people are having problems with.

Another tip from the DH forums: Bayesian filtering won't kick in until it has learned at least 200 messages of both spam and ham. To check the levels:

sa-learn --dump magic