Vittorio came by my office around a year ago and asked whether it was OK for him to write a book on CardSpace. "Oh course" I said, and this set in motion a lot of work to make this thing happen. "Understanding Windows Cardspace" was complete late last year and it is now on the shelf.
He has also just posted a video on Channel9 on the subject which can be found by clicking on the link, where he is chatting with Caleb Baker about CardSpace in general and the book they wrote. The post can be found here or clicking on the image at the top.