There are a few simple reasons why MbUnit is still not the most widely use Unit testing framework:
The GUI is still not as user friendly as it could be. that is - it is too complicated. in my mind it should look *exactly* like the NUnit GUI so that people can relate and use easily.
No TestFixtureSetup and TestFixtureTeardown attributes
I'm thinking that if at least the first 2 are fulfilled - I could start using MbUnit in my next project. Right now it is in a place where RSS bandit was a few months ago: Loads of nifty features and abilities but still needs a little nudge to be usable for the masses. Way to go Peli!