In my experience, node.js is a terrible choice for most web applications. If you really need real-time, sure, go for it. But if you're interested in node as an alternative to rails/sinatra/django/flask, then stay away from it. The cool stuff you get for free like coffeescript/jade/stylus can also work with the ruby and python frameworks.

Node sucks for general web apps because you have to program everything asynchronously. This is a major step backwards, and quite frankly it feels to me like trying to program in assembly. It's not expressive at all. You have to write your program in some pseudo code, then translate that to async code. And what for? What's the advantage you'll get? scalability? Who says you will need it? This is exactly where you should remember that premature optimization is the root of all evil.