We used MsTest framework for a project that mainly had integration tests for Wcf Services, and found particularly useful to use AssemblyInitialise method to start the services hosts before all the tests are run and AssemblyCleanup to stop all the hosts after all the tests in the assembly have run.
At some point, the company decided they would like to change this project to use NUnit instead of MsTest (for sake of uniformity, as all thi other project were using NUnit).
The only problem that I saw there was that I didn't find any easy way to simulate this AssemblyInitialise and AssemblyCleanup methods.
But here we are saved, as someone told me about this SetupFixture which works like this:
The class with this attribute can contain a SetUp method and a TearDown method.
The setup method from the Setup fixture is executed before all the tests from a namespace are executed, TearDown method, after all the tests in a namespace are executed.
This was very useful for out DB integration tests as well, as we needed to setup database stuff before executing all the DB integration tests.
So here we are, saved and NUnit is still better than MsTest ! (but not better than MbUnit , imho) :)