WS-Federation and Project Liberty interop

I guess this is a result of the new friendly relationship between Sun and Microsoft:  A document on MSDN describes how to interoperate with Project Liberty.

Project Liberty is Sun's challenger for Passport, Microsoft's single-signon mechanism.  I want to see some single-signon mechanism take off so I can use it on my own sites; I don't care which one.  Microsoft charges for Passport, which rules it out for me.