Top 10 is impossible to say since we don't know who will be in those slots 5 years from now. Internet time is insanely fast. Things come and go very quickly. I think it'd be fair to say half of the Top 1000 sites will be with the rate of Node's current development. Development is now getting to a point where they aren't going to be adding new features, but focusing on making it as efficient as possible in what it is (give this a listen http://javascriptjabber.com/052-jsj-node-npm-with-isaac-schl...). I made the switch recently from PHP and I don't think I'd ever go back. Love it, although yes there is a slight learning curve but if you know Javascript already you'll do fine. Knowing how to use callbacks and using some sort of middleware like express is the way to go when developing applications with it.