You really don't want to just do a quick convert, you're not going to get the most out of it. CoffeeScript has an idiomatic way of writing it, and I haven't seen anything that can match hand coding. http://arcturo.github.com/library/coffeescript/04_idioms.htm...
You can use something like http://js2coffee.org/ , and it's OK, but it doesn't always make the best choice.
Hope this helps, and I can't wait to see what the 'pros' think!
Does the lack of such tool make working with cs code harder? Specifically I mean maintaining and refactoring such code.