ScottGu posted some tantalizing screenshots of the System.Web.MVC project properties that allow you to pick the target unit testing framework that you would like to use for your project. Choices in the screenshot are MSUnit, NUnit, MBUnit and XUnit. It's quite nice to see Microsoft embrace community efforts in this project. My feeling is that the recent hiring of several prominent open source advocates by Microsoft is what is starting to change this mentality. This screenshot has been causing some favorable reactions in the blogsphere (Phil, Jeremy).
My prediction is that community supported unit testing frameworks will be integrated into the VSTS/TFS suite by the end of this year. Here's hoping that ScottGu and Brian Harry can make this happen.