Here is a link to a great panel discussion on the merits of Coffeescript and Dart. A pretty heavy duty discussion but worth reading if you are thinking of picking up a new language.
And for a great comparison between CoffeeScript, Dart and JQuery, check out this post.
My hope is these languages will be the answer to the big problem in development right now – the cost of developing apps for the various mobile platforms. I dare to dream that Icould write code in one language that compiles to run in the different phone operating systems.