I've definitely done the separate channel thing in the past for update notifications and it does perform very well.

Our setup is a pub/sub system, where the "sub" happens implicitly with the request for a resource via the GRIP proxy and protocol and the "pub" happens when we update our models as well. The proxy acts a lot like node.js and Socket.IO would, but simply speaks pure HTTP on our RESTful resources instead of the Socket.IO protocol over their transports.