Django: JSON Notifications using Redis PubSub, Node.js & Socket.io
I'd definitely not use node.js for this. You can handle websockets in Python just fine, with Celery or gevent or whatever.
Just create a thread which registers to Redis and listens for new messages.
When the user connects, put the socket into a weak-value hash indexed by the user's name; when a message for them arrives, look up the destination username in that hash and send it off. Weak-value because it cleans up after itself when the user disconnects. Simple, really.
I'd also send new messages to the server using the websocket instead of HTTP-PUT.