Jeremy Miller asks that question in this post.
I haven’t had a chance to use it on any projects, but I really like the idea of customer-facing tests. Miller describes them very well as “executable requirements”. The comments highlight a number of alternatives to Fit, including FitNesse, Green Pepper, and ZiBreve.
From the comment volume on Miller’s post, it seems that only the specific implementation of Fit is on its way out. The idea looks very much alive.