I attended a presentation by Kim Cameron who has a blog all about Identity. It was a really good albeit short presentation on the Laws of Identity and how Microsoft Cardspace (ships with Vista) addresses that. One interesting statistic I learned from this (apart from the excellent content of the entire presentation) was that:

1. Microsoft Passport was an internet failure as far as a global identity/authentication scheme went.
2. Microsoft Passport was a success for Microsoft as a microsoft only identity/authentication scheme.
3. There are approximately 1 billion logons per day that utilise passport. Thats right. 1 Billion.
4. Passport has approximately 300 million users.

Thats a bucket load of requests and users in anyones language. Pretty staggering stuff to think about.