So I wrote about spam the other day. POPFile is one of the core tools in my personal spam fighting toolbelt. I use it in a chain of spam fighting tools, where SpamAssassin has a rule that scores mail higher if POPFile has scored it spam. Really and truly, though, I could use just POPFile by itself and it would be plenty sufficient. After training it for a few days, it has > 98% accuracy, and this includes not just a spam/nonspam distinction but filtering into 12 buckets, only one of which is spam.
Version 0.19.0 is now out and available for download. I highly recomend it.