I'm too am comfortable with Rails and the Ruby ecosystem but jumped into Express recently with Socket.io and MongoDB and think you should too. My curiosity was shortly satisfied and I decided to stick with synchronous code instead dealing with callbacks. For a moment there, I was high with "I'll use Node with everything!".

But the experienced inspired me to play with Ruby's EventMachine, Cramp, Goliath, and implementations like socketio-ruby on Cramp. I also took some time out of my life to really dive in to Javascript and experience some new tools.