Update: It looks like the post is too long for some people. So here is TL;DR: Node.js's sweet spot is where the server side is for integration work of fetching data from other sources (e.g. database) and when javascript is already used for the client side.
So, node.js is a hot topic now. I wanted to share some of my views about this framework, some misconceptions related to it (IMHO) and maybe help deciding when to use it. If you find any mistakes, please comment!
The first thing I want to discuss is the misconception (again, IMHO) that evented IO is more performant vs thread IO. Here is what happens when a process does IO (simplisticly):