One of the reasons why we picked CoffeeScript over JS for Zucchini was its readability.
It takes a bit of effort from a QA or a QA + Developer pair to come up with initial screen elements and actions definitions. However, the end result is more maintainable and it's is easy for a QA's to come up with new features based on existing screens. It also gets simpler for him / her to come up with small fixes without being lost in the JS code.