EDUCAUSE has released "7 Things You Should Know About Federated Identity Management."
Here's an excerpt :
Identity management refers to the policies, processes, and technologies that establish user identities and enforce rules about access to digital resources. With an enterprise identity management system, rather than having separate credentials for each system, a user can use a single digital identity to access all resources to which the user is entitled. Federated identity management permits extending this approach above the enterprise level, creating a trusted authority for digital identities across multiple organizations. It results in greatly simplified administration and streamlined access to resources; eliminating the need to replicate databases of user credentials for separate applications and systems offers improved security. Federated identity management puts the focus on users of information and services rather than on entities that house those resources.