The problem with Node.js is that it's very good at it's original purpose and terrible at everything else. Node.js is excellent for building network services. It is terrible at general server-side computing. If you need a server that consumes websocket connections, it's great. If you need to build a CLI script that installs and upgrades various software packages, not so much. If you need a chat server, it's great. If…
My latest project runs Python/Pyramid and MongoDB for the more traditional computational stuff. We have a notification architecture running through node.js/socket.io sending real-time events down to the browser.
It works beautifully.
All of that COULD have been implemented within the Pyramid layer (or Twisted..or whatever), but it would have been much more difficult and time-consuming to do.