Very, very rarely. Along with "now you can get your frontend developers to write backend code!", it's one of those oft-cited but spectacularly bad reasons to start using JavaScript for non-client stuff.

In saying this, I use node for a heck of a lot at work, but that's mostly because some of the workflows available (streams and events specifically) are perfectly suited to the programs I write in it; not because it lets jQuery monkeys crank out substandard backend code.