I have about three dozen, but most of them are 'special' addresses, created on the fly for SpamGourmet, which offers an unlimited number of free email addresses to use for such things as web forums, online ordering, etc. They all get forwarded to a single account, though. http://www.spamgourmet.com/index.cgi
As for accounts I use actively, probably four. Two from my ISP, one from MyRealBox and one from SpamCop. Just about everything gets forwarded through SpamCop, though, so it's not like I have to check a bunch of different accounts.