Great stuff!!
So, do you open up 2 channels? One for the client to make calls to the server (this could just be normal HTTP) and one for the server to make client calls?
Depends. We're built on top of Socket.IO (http://socket.io/) which uses a websocket connection when possible. It falls back to assorted other transports if websockets are not available.
And in the next release of Socket.IO Guillermo has promised us multiple channels, so projects like nowjs should get channels for free!