It is hinted in the article that node.js is better for some use cases than others.  One thing node.js is good at is realtime apps and socket.io and the evented model make these easier.

However, as a server developer guy too, I must point out that if scalability ( or premature optimization ) is dear to you, I would look further than cluster to run multiple node processes. A good solution I found for a few projects is to use Redis pub sub to encapsulate socket.io messages to connected clients to make it easy, non-blocking and performant to scale to multiple nodes. For a project where I have some potential CPU bound code, I further split these operations in another process (let's say a game state machine with calculations) with which I exchange pub sub messages. In such realtime apps, the worst that can happen is that some process intensive functions may take a bit more time to dispatch information to the clients but the core communications node processes won't be blocked and will be screaming fast and horizontally scalable.

I've found that Redis pub sub is awesome for simple and fast interprocess communications.