Getting in front of the problem

Mostly I've been observing the problem from the ISP side, but the simple countermeasure that seems to work is to make it slower and more expensive to get accounts (or domains). What this means in practice is that the more responsible companies, the companies that are making it harder for the spammers, are put at a competitive disadvantage to other companies that can grab at customers based on more convenient registration processes.

The obvious solution is to agree on standards for registration processes, and cut off the ISPs or domain registrars who cheat on the rules. If the basic rule required all customers to put up $10 up front for a domain, and required that the domain could not become active for 24 hours after registration, then at least much of the current abuse would be stopped. Of course the scammers and spammers will continue looking for other creases, but the anti-spammer standards can also change.