What's so elegant about that if a spammer with elementary knowledge about SMTP and DNS can easily bounce his stuff off of any of the thousands of unsuspecting hosts and/or use unsuspecting forwarding name servers in the slave mode?
http://www.sendmail.org/antispam/ has the answer to that. As we find these servers (which means: as they are used as unintended relays for the forwarding of spam) we educate their owners and they upgrade. Or they get blocked during spam episodes, which process will shortly become automatic. eBGP converges quickly enough that I can inject a /32 and have it in 4 countries in less than a minute. They rotate phaser frequencies, we rotate shield frequencies. And while the war of escalation goes on, providers are educated -- and that's the real goal, so no matter who's "winning" at the moment, *I* am winning.