Roughly 2000 virus emails hammer me every day: clamav keeps me happy. Roughly 200 spams arrive per day: SpamAssassin keeps me happy. 82% of all the email I get is unwanted. That is more than 11000 emails per week I'd rather not get. Only a very minor fraction of those mails actually end up in a mailbox I read.
It turned out that only doing Bayesian filtering to catch spam, such as Bogofilter, is not good enough for me.