The sweet spot for node.js to me would seem to be soft realtime applications. For example you might build a twitter clone where you wish for new tweets to be au

The sweet spot for node.js to me would seem to be soft realtime applications. For example you might build a twitter clone where you wish for new tweets to be automatically pushed to the browser via JSON/Websocket etc. On the backend you might implement a pub/sub system where events are raised upon a tweet being made and these events are filtered into different queues. So you might implement a waitForNewTweet() function which will wait for an event on the queue. But this method could take a very long time to return, and all of this time the client is holding open a socket on the server. If waitForNewTweet() blocks then that thread will no longer be able to do other work, so each client must allocate a new thread. So if you have many client connected for long periods waiting for tweets then that is going to be a lot of threads.