I have tried it, and I love it (same goes for Backbone and Underscore, by the way - you are the developer who's work has impacted me the most positively in the past year) but I haven't used it for anything serious yet, and here's why: the workflow is more complicated than "make change, refresh". Until very recently, my programming time was split about equally between the three major operating systems (I have since managed to phase out Windows almost entirely) and it's way more trouble than it's worth to set each of them to autocompile changes to .coffees. I know that I could import the compiler and use script type="text/coffeescript", I know about LiveReload for Mac (even though I couldn't get it working in the few minutes I tried it) but the bottom line is that I already know how to write Javascript, and it works great. Learning a new language is the sort of thing I like doing, but wasting time futzing around with build systems is not.
Anyway, I didn't mean to rant. I could easily love CoffeeScript - I don't feel threatened by it a bit. But there are some serious barriers to adoption, and Javascript isn't nearly painful enough for me to deal with them.
If that's truly all that's stopping you, try out Middleman (http://middlemanapp.com/) or my own Draughtsman (https://github.com/stdbrouw/draughtsman). Taking two minutes to install an app hopefully does not constitute "wasting time futzing around with build systems" :-)
Also, I think your problem is very particular to front-end devs and designers-that-code. If you're already doing back-end in your framework of choice, adding CoffeeScript or any kind of precompilation into the mix is usually just a one-liner in a config file away.
And not every back-end dev is lucky enough to be working in their framework of choice ;) (I would actually call myself more of a front-end guy, but I do plenty of back-end work and the only time I get to use frameworks I enjoy - Django, Flask, etc - is for my side projects.)
I have tried it, and I love it (same goes for Backbone and Underscore, by the way - you are the developer who's work has impacted me the most positively in the past year) but I haven't used it for anything serious yet, and here's why: the workflow is more complicated than "make change, refresh". Until very recently, my programming time was split about equally between the three major operating systems (I have since managed to phase out Windows almost entirely) and it's way more trouble than it's worth to set each of them to autocompile changes to .coffees. I know that I could import the compiler and use script type="text/coffeescript", I know about LiveReload for Mac (even though I couldn't get it working in the few minutes I tried it) but the bottom line is that I already know how to write Javascript, and it works great. Learning a new language is the sort of thing I like doing, but wasting time futzing around with build systems is not.
Anyway, I didn't mean to rant. I could easily love CoffeeScript - I don't feel threatened by it a bit. But there are some serious barriers to adoption, and Javascript isn't nearly painful enough for me to deal with them.