Internet2 (the US networking consortium for the research and education community - akin to Janet in the UK) has just announced a Shibboleth collaboration project with Microsoft, to develop interoperability with the Windows CardSpace system.
Before we go any further, let's deal with the basics:
Shibboleth is a federated authentication architecture - it allows users to have one set of login credentials across different systems, rather than having to have loads of usernames and passwords. There is a fantastic video animation on the JISC website that puts this all into plain language
Windows CardSpace is a user-based system which allows users to store their credentials and pass them across to systems at their choosing (an example is that you can store your different online identities in CardSpace, and pass them over to websites as appropriate - for example logging into a website, or providing credit card details)
The collaboration is described as "a very important step forward in creating a ubiquitous Internet identity layer" (hip, hip hooray from those of us that can't remember 642 different usernames and passwords, and as a result end up using our first cat's name as a password on too many websites).
This is really important in the world of higher education, where the need for identity management in intra-institution systems is almost as wide as the need for inter-institution ID management. And is becoming increasingly important across the rest of education, as the need grows to provide a single identity for students to be able to access learning resources in school, from home and anywhere else.
All of the details are provided on the Internet2 website