My personal experience with bogofilter has been quite positive. I am currently actually using a combo of that and spamassassin. Between the two of them, I've got only one spam in my inbox so far this year (and 160 in my spambox). I have only had one problem with a false positive, and that was from someone using a skytel pager email thing (quickly fixed with whitelisting and score weighting).
(no subject)