Native Promises already landed Chrome 32 and Q still does not support native promises. Bluebird delegate to native if supported.

Promises can be used as flow control, but more importantly, it's an object that encapsulates asynchronous mechanics.

I like to see how async can launch an asynchronous operation, then allow listeners to be attached later to capture the result. Now, you may say that if you want to attach listeners to capture result, you'll want to use event emitters. True, but event emitters has its own problem because event emitting and attach listeners are synchronous. What if the event was emitted before any body has a chance to attach listener to it?

Promises does not have these issues.