Well,
I have been using TDD for Sharp3D's development process for few days now and it already helped me find several bugs.
At first I thought having to write all the tests code will just be a waste of time I could spend on adding features to the library but after some actuall work I noticed that working on the tests isn't time cosuming as I thought and it helps me find some bugs I wouldn't find otherwise and deliver a better product.
Having said that, I really have to say that the testing and refactoring capabilities in VS2005 are awsom. I only wish they would add performance testing capabilities (So I can define “test methods“ that would run and be time measured).
Oh and btw, notice the new Stopwatch class used to accuratly meaure times (for peformance etc...)