[Update: Adding the link - thanks Dumky]
A great write-up of the WS-Federation Passive Requestor Profile Interop Workshop was posted on the Web Services Developer Center today. Passive Requestors are things like Web browsers and the WS-Federation Passive Requestor Profile has to do with authenticating browser clients in a federated security evironment. There is a nice overview of what the profile is all about and how well the implementations worked together. IBM, Microsoft, Netegrity, Oblix, OpenNetwork, Ping Identity Corp., and RSA Security all provided implementations. The results:
high levels of interoperability between all implementations from all vendors participating, and this was achieved much more rapidly than expected.