I've used node, and I just don't see it.

You can share fragments of code, but for reasons of both security and logic not much more. In my view, the evented nature of node negates most of the pluses of one language.

Additionally, javascript is a shitty language if what you want is a large amount of business logic. Python and ruby are much more concise and expressive. This is a huge win that a lot of people overlook.

Now, if you need to throw together a chat service or push service really quickly, I see the value, but that's about it. Of course for that, I'd just use clojure or java.