The debugging issue is the only cons of coffeescript. I hope the new coffeescript compiler will solve this issue and offer us sourcemaps.
Debugging with CoffeeScript can occassionally be a challenge, that's true. The benefits more than make up for it: concise and readable makes a big difference to me.
CoffeeScript has issues. First of all debugging the compiled JS in a browser is a catastrophy (compared to debugging vanilla JS). Second of all I have no (really no idea) why inventors of the language did not add type system, since in my opinion that is the main thing that JS lacks. Nevertheless it's pretty fun to use. It is _really cool_ that the whitespace matters.