More investigation with my test app shows that the 'connect' response is being received from socketio, but the subscription requests are completely ignored. No 'subscribe' response ever gets returned.
I thought it might be something to do with my IP? That Mt.Gox was blocking my connection; but I routed packets via both home and work internet connections and the result is the same.
Unfortunately, the connection has been spotty for a couple days. This is especially disturbing during the days following the TradeHill announcement -- it would be nice to see how the markets are responding to it in real time.