Node JS rocks when it comes to io. Club it with Nginx and you get scalable systems. IMHO NodeJS/Nginx lets you get most out of your hardware. My experience is limited to using it for io based operations and dude it rocks. The only glitch i see is that it is hard to write object oriented equivalent code. Just create an eco system of small serverices that is built on NodeJS
I have not used node JS for projects having high computing requirements (read processing requirements). There are now a lot of libraries and different ways of dealing with such things in Node, but i have not tried it myself. It would be interesting to see if any one used Node for projects having high computational requirements in production and how it scaled and what challenges they faced.
In this world, alas there is no single tool for all different problems and we need to acknowledge it