FTA "My first version was hosted on Heroku and lagged like crazy."

Hmmm even on heroku you should have pretty damn good responsiveness as I assume it should be using what is known as "COMET" http://en.wikipedia.org/wiki/Comet_(programming)

The polling is just to reestablish the kept alive connection. Which while still less than ideal... I wouldn't think would be terrible.

Not saying the author is wrong but being that it seems like his first foray into socket.io it's a possibility.