I can personally vouch for the maturity of Node especially Socket.io. We're building a web-based email client that relies heavily on real-time communication with a Node-based email importer. See http://philterit.com. I've found Node to be faster and more lightweight than Rails 3, which we initially used for our prototype. With JavaScript being the lingua franca on the client-side, specializing in it as a team has permitted us to master it and offer a far better user experience.