> function applications require parens and which don't.

Yes. An understanding of JS is definitely necessary when developing with CoffeeScript. The ambiguity that the parser allows sometimes leads to code generation that isn't at all what you intended. I sometimes find myself going into the JS output to make sure the compiler did what I intended.

Annoying, but at least for me, the benefits of cleanliness and things like list comprehensions and Python-esque list semantics makes it worthwhile.