Spammers Weep: DomainKeys ID Is Good To Go
1) Mail servers running the DomainKeys ID technology will insert a digital signature into the header of each outgoing message.
2) When an email is received by a DomainKeys ID enabled mail server, it will check to make sure the ID is accurate
The spec doesn't really say what to do next, but leaves the choice in the hands of the ISPs who'll probably be able to integrate DomainKeys ID with their existing anti-spam measures. If this turns out to be the case the upside is that even if spammers can/do circumvent the new technology, they're right back to where they are today.
If the technology really takes off, it would also seem that it could have a largely positive impact on email spoofing. Let's keep our fingers crossed that our days of getting more spam than useful email are drawing to a close.