My former colleague Jim Matthews presented and wrote an experience paper for using FIT acceptance testing on development projects that describes the workflow that we used at my prior job. Nicely done Jim.
We were able to almost completely test an asynchronous messaging broker inside FitNesse acceptance tests. We also used it extensively to describe business validations and routing logic within the larger system. The office evaporated before we retrofitted the rest of the application with automated test coverage, but we were well on our way.