The MSCOM Team has done a post on their blog about their experience with Active Directory Federation Services (ADFS).
ADFS is a Windows Server 2003 (R2) component that facilitates a trust between two or more organizations that will allow the sharing of multiple resources while maintaining each organizations ability to manage their own set of users. One of the significant challenges faced when trying to implement any new solution is simply keeping the system available. In our implementation of Active Directory Federation Services (ADFS) this was one of our key focuses in moving forward with the project. The ability to use single sign-on for ADFS aware applications is a huge benefit, however it can become a painful burden if the service is unreliable.
Read more: Microsoft.com and its ADFS Implementation.