Knock, knock, who's there?
Leigh Dodd's presentation to the Society for Scholarly Publishing in San Francisco back in June provides a nice sketch overview of the federated access management problem space, ending with a brief, two-slide, summary of Shibboleth vs. OpenID as possible solutions. It would be nice to have seen more discussion around these final two slides, particularly touching on the 'trust' issues... but that would have probably made for a different, and rather more detailed, presentation!
Definitely worth a look.
PS. Leigh's DRM: a Skeptic's View is also worth seeing.