Ask HN: People experienced with Node.js ... what downsides should I be aware of?

This is a rather open-ended question and I'm hoping some folks with a good deal of experience will be able to help me out here. On paper I quite like the idea of NodeJS. However I'm new to Node and want to learn from your hard-earned experience. What kind of pitfalls, downsides, or gotchas have you come across when working with NodeJS?