What we really need is senderID up and running with the patents dropped... we need very public black-lists of bad domains/IP ranges and we need the ISPs to get off their collective asses and to do something about zombies. Like limiting machines in their
network to sending 500 e-mails per day per machine (using IDS type devices).
Allow people to opt out of the 500 message limit by paying £1 per month. That way the clueless bunch who get infected by zomies will only be able to send out 500 spam a day each, and the ones that opt out should be able to defend themselves.
All of this will of course 'solve' nothing, but with it you should expect a massive reduction in global spam (-20% in a year).