Ask YC: Best language/framework for comet intensive app

I'm looking at building a web-based chat app. Instead of having clients poll the server (ajax) I would rather use comet to have the server push updates to the clients.

I've looked at a few implementations, lift (http://liftweb.net/index.php/Main_Page), turbogears using orbited (http://brbx.com/orbited/).

It's still in the planning phases, no language chosen yet. Just wondering what others have found success with.