I've been playing with the unit testing in Visual Studio Team System (documented here), and it's awesome! The parts I love the most are:

• Integration of the unit testing framework with Visual Studio
• The ability to select some code and have it generate the skeleton of your unit tests
• The integrated code coverage. I love that you can run a test and then see which lines were hit and which weren't right in the code editor!

There's been a lot of feedback to include the unit testing in the basic version of Visual Studio.