Many, many people think that Test First approach is not working and not intuitive at all (especially for acceptance tests). They have a point when say "How could we test something if we don't have implementation and even system specification?". Yes, if you don't have requirements, you can't test. But they don't understand that acceptance tests ARE that spec. It is not wise to artificially separate User Stories from Acceptance Tests. They may be in one place and make up the spec. And even more, it should be executable spec. FIT is one of the closest solution to make spec executable. The tricky thing is to make acceptance tests creation as informal as possible, while keeping them executable. FIT provide a mix: you may write some informal sentences in Word doc, then create a table that will contain test harness. While the first part is simple for customer, the second is not and should be created together with developer, QA or someone who have experience with FIT.
Is it possible to make acceptance tests creation process simpler? Less formal? Intuitive? That's an interesting challenge!