In my experience, it took essentially zero time to understand and be able to write simple CoffeeScript. Yeah, it will take some minor effort, but I see it as as parallel to templating languages in terms of your argument. It is faster and cleaner to write, and makes my life easier. I have hardly (I think never) needed to look at the output for debugging, but when I have looked out of curiosity it seemed reasonable, just with strange variable names.

Does anybody have examples of some CS code that only differs from JS in terms of syntax (eg. not defining a class or something) but compiles to something weird?