I've been reading some on SAML, the XML language for passing authentication information around the net.  SAML, as one would expect from an XML based language doesn't do authentication, it is merely a standard for passing authentication information and user attributes from place to place. 

There's a pretty good article from Sun that gives some actual code examples (always a welcome addition) as well as the standard itself. 

I'm still not entirely clear on how this all relates to other initiatives such as MS Passport and the Liberty Alliance.  It is clear that SAML is not at odds with those projects.