Well I'm relatively happy with dspam's performance squashing spam -- one of my friends sends out a mass-mail from yahoo every so often, and that's been the only false-positive so far.
The only major problem is the time that I tried to bounce myself a large 5Mb attachment, and dspam could do was make gasping, wheezing, choking noises. It started failing with EX_TEMPFAIL, a sendmail error that means "try again later". I think that the program just can't handle large large files. I had to delete the spooled mail and fix a lockfile problem for it to start working again (which it did). Interestingly, while in a failed state dspam just waved on through all the incoming mail, so I had a much larger number than usual of spam messages to deal with. I suppose that is the "correct" thing to do, since it gives you a strong clue that something
is wrong and you'd better go investigate it.