There are just too many posts aout Node.js these days that lies on the extremes so I want to put my 2c in the pod as well.
My first hand experience with Node.js was when I did my summer internship at Intuit last year. I did an innovation project with it to introduce the language to other developers there in the office. I ABSOLUTELY loved it. It was very low on memory usage and very easy to code and interact with other web services and it IS fast against apache for simple tasks. But as the code base grows it gets increasingly hard to manage and the chain of callbacks gets messy even if you use awesome libraries such as Step.
Personally, I think Node.js is awesome to develop real time applications that does not require long blocks (process api calls) and it is not ready to use as the primary language yet. You still have to fall back to the more mature languages.