How can I imitate Stack Overflows SSO? Particularly where it federates with serverfault.com?

Question

How does Stack Overflow's SSO work? ... whatever it is they are doing it seems to work for all sites in the network.

I'd like to learn what Stack is doing so I can see if it's possible to get a similar registration scheme between http://perfmon.com and http://eventvwr.com under ADFS. I understand that SAML and OpenID are different animals, but the concept of transparent registration should be the same.

Q: How does Stackoverflow "federate" with the other sites such as serverfault?

Answer 1

OpenID, One Year Later on SO blog explains how do they solve the problem.

Also, there is a post on the new Global Login Mechanism on the SO blog.