Brian Keller has just posted information about a new case study highlighting a company that achieved CMMI certification by using Team System. He writes:

We have just published a new case study which helps to underscore how Visual Studio Team System can assist organizations who are seeking CMMI appraisal. This is a great example of how the integrated data warehouse, artifact linking, reporting, and other capabilities of Team Foundation Server allows for clear traceability, auditing, and ultimately better quality assurance across the entire software development lifecycle.

In the case study, the technical architect is quoted as saying:

With Microsoft Visual Studio Team System, we can adopt more of a team approach to software development and benefit from tools…that support the entire software life cycle.

I don't think it could have said it better myself!  I'd encourage you to take a look if you're interested in achieving CMMI certification.