We recently published another great case study of Team System adoption, this time outlining the benefits in productivity realized by the development team at Getty Images in Seattle. Here's the abstract:
Imagery, film, and digital services provider Getty Images was losing thousands of hours of software development productivity per month due to a slow and unreliable source code management system. The company switched from MKS Integrity to a software life cycle management solution based on Microsoft® Visual Studio® 2005 Team Foundation Server, a component of Visual Studio Team System, which eliminated all major problems faced in the past. Better performance, reliability, and ease of use have improved software quality and made the development group 10 to 15 percent more productive. New collaborative abilities enable people to work more closely together, and improved reporting allows them to monitor project status and progress at a glance. Moreover, the move to Team Foundation Server cost less than it would have to stay with MKS Integrity.
If you or your team is evaluating a possible move to Team System, I'd suggest you take a look at the specifics of Getty's experience with Team System.
Update: I just found out that this case study is no longer available due to some complications with the PR agreement required for us to tell this story. When things get straightened out, I'll post another update. In the meantime, you can find other Team System case studies here: http://www.microsoft.com/casestudies.