I went to a panel discussion moderated by Doc Searls on open source issues and identity.  The part I was most interested in was Ken Klingenstein's talk about Shiboleth.  Shiboleth is an interesting word what was used to distinguish the Ephraimites from the Gileadites. The Ephraimites, not being able to pronounce sh, called the word sibboleth. (See -- Judges 12:4).  From the introduction:

Shibboleth is an initiative to develop an open, standards-based solution to the needs for organizations to exchange information about their users in a secure, and privacy-preserving manner. The initiative is facilitated by Internet2 and a group of leading campus middleware architects from member schools and corporate partners. The organizations that may want to exchange information include higher education, their partners, digital content providers, government agencies, etc.

Shiboleth, as I understand it, is open-source, enterprise middleware that manages authorization for users other enterprise services.  Sounds similar to SiteMinder.  I wonder how it compares.