The compilation step completely defeats the point of rapid prototyping in Node.js. I'm really used to just modifying my .coffee files to get the resulting .js files compiled instantly and transparently to me.
Closure does a great job in static analysis. It's not obvious, but Clojure's library is HUGE and has to be pruned of unused resources.
On the other hand, it's not very convenient for the developer because Closure's job takes a LONG time. I guess this is where this project comes in.