There is a discussion on this issue here: http://storyq.codeplex.com/discussions/256021
The current implementation is problematic because earlier 'Given' and 'When' functions set things up for assertions in the later 'Then' functions. When the earlier functions throw a 'Not-Implemented' exception it is likely that there will be exceptions in the later functions, like NotImplementedException, when asserting on complex objects that are set up in the earlier functions.
In this situation it makes it hard to implement tests first and still have a passing integration build. It is very important to be able to tell the difference between tests that are failing because something changed and tests that are "failing" because they were simply written before the implementation is complete.
Please fix this. It hurts nothing and helps those of us trying to write test first.