Via Rajesh has this list of links from MSDN that should help most people who want to find out more about CardSpace:
Introducing Windows CardSpace This article introduces the set of new Windows capabilities called Windows CardSpace (formerly “InfoCard”), which provides a standards-based solution for working with and managing diverse digital identities. A Deeper Look at Windows CardSpace In this Security Briefs, Keith Brown drills into Windows CardSpace (formerly “InfoCard”) and demonstrates how to create a relying party and a client. Video: Windows CardSpace Explained Ever wonder what Windows CardSpace (formerly “InfoCard”) is all about? Nigel Watling (Technical Evangelist) and Andy Harjanto (Program Manager) explain it in this Channel 9 video with a lot of time spent on the whiteboard. Getting started with Windows CardSpace Step by step instruction on how to build federated identity applications using Windows Communication Foundation and Windows CardSpace (formerly “InfoCard”). In addition, this new Federated Identity & Access Resource Kit for Sept 2005 CTP includes samples to build Security Token Services (STS). (Link currently broken – Kim) Introduction to Information Cards and Internet Explorer 7.0 (in C#) This sample contains 4 exercises demonstrating how to use CardSpace to get a digital identity from a user via Internet Explorer, updated for RC1 and beyond. Included in this sample is the code to the TokenHelper class, which allows relying party websites to decrypt security tokens. The Laws of Identity Defining a set of fundamental principles to which any universally adopted, sustainable identity architecture must conform, the “Laws of Identity” were proposed, debated, and refined through an open and continuing dialogue on the Internet. Microsoft's Vision for an Identity Metasystem The Identity Metasystem is an interoperable architecture for digital identity that assumes people will have several digital identities based on multiple underlying technologies, implementations, and providers. Channel 9 Interviews Kim Cameron The folks from Channel 9 talk to Kim Cameron about identity. The Identity Blog Check out Kim Cameron's Identity Weblog where he discusses the Laws of Identity and other topics around Web services and identification. A Guide to Integrating with Windows CardSpace v1.0 Learn how digital identities can be integrated into a user-centric identity framework, based on the concept of an Identity Metasystem, which promotes interoperability between identity providers and relying parties with the user in control. A Technical Reference for Windows CardSpace v1.0 in Windows A technical reference for the schema employed by and the mechanisms implemented in the Windows client Windows CardSpace (formerly “InfoCard”) system. A Guide to Supporting Windows CardSpace v1.0 within Web Applications and Browsers Learn about the web interfaces utilized by browsers and web applications that support the Identity Metasystem. The information in this document is not specific to any one browser or platform.