If you could do this over again, would you still choose socket.io for websockets, or would you go with something else like PusherApp?
Today I'd consider going with a service, but first I'd see how https://github.com/LearnBoost/websocket.io looks. Most of our problems have been with abstractions in the socket.io client and scaling issues with server process chatter. The chatter shouldn't be necessary with websockets-only.
The socket.io codebase has been shrunk dramatically, and it's as a result easier to scale/maintain.