When to use node.js?

So, I've been reading a few articles and googling this question, and not arrived at a practical answer. I get the advantages of using it, but what would I use it for?

One tutorial I started reading showed how to implement an http server in it...which failed to make sense. Why isn't it an apache module?

The best I can reckon is that you wouldn't serve pages from it, just data. A feed, an API, just processing. Does that make sense?

Taco's been getting really into node.js, maybe he'll stop by and give his two cents.