You know you’re seriously an identity geek when your spare-time reading is Understanding Windows Cardspace. But for this rapidly rising new branch of the digital identity space, a book with this much good information about Microsoft’s CardSpace technology is definitely worth the investment.
About half the book is background on the entire problem space that information cards are a solution for; it’s long but worth the read. The rest is technical meat that there are few other places to get.
Recommended especially if you want to move into this new space quickly.