Spam feeds on monocultures.
Standardized email systems, Windows SAMBA messaging and other chat, widespread blogware (MT), all have been targeted and hit by spammers. Defense mechanisms have developed, but then shared and deployed across the monoculture, forcing spammers to react. Those spammers that successfully adapt then have the full monoculture to abuse again, forcing another iteration of the development cycle again.

Fight spam with biodiversity.
Spam economics rely upon the wide distribution available from a monoculture. Destroy the monoculture and spam will have to become intelligent enough to test defenses, evaluate responses, and calculate the cost/reward benefit of continuing the attack.

Keep anti-spam techniques local.
Either code your own anti-spam engines, or talk with your friends about anti-spam responses and adopt their good ideas. This should start to break up the monoculture. Even better would be to break anti-spam code into exchangeable (within a trust network) snippets that we could recombine, granted that would require a common code platform that we don't have (hence why we developed open standards in the first place). Funny that, eh?