Your errors list JS line numbers. I didn't find it very difficult to mentally map the JS errors back to my Coffee source though - you get the same program structure and variable/method names before and after compile.

Let's say you found a bug in line 41 of my JS source here: https://github.com/dpritchett/chatbox/blob/master/public/cha...

Digging into the Coffee source shows the same short method with all the same identifiers and the same basic structure... just less boilerplate: http://dpritchett.github.com/chatbox/docs/chatbox.html#secti...