Last time I played with RhinoMock , I was in state of shock and awe. I was awed because it improved my design. It requrired that the code under test should to be isolated from rest of application. That was done using Interfaces . Contract based programming is always best way of programming. I could test behavioral aspect of my code.It would have been little difficult using xUnit framework. It was almost creating a simulation flight envrionment and enjoying the pleasure of real flights.
I was also shocked by the fact that my behavioral tesing Line of codes were many times more than code under test.
I was left in no doubt that Mocking is very powerful and advance technique of TDD. Also at the same time, It will make selling TDD difficult to people new to programming.
Hopefully Lambda expression may help in that direction.