I'm using it for a production site. It's been live for a few months and I've had no issues with the node runtime. Stick with the latest stable release (currently 0.2.6).
The 3rd party modules written by the community are where you may run into issues. Some modules are more stable than others. The node community has standardized on github, so it's pretty easy to fork and fix things you run into. But be prepared to roll up your sleeves and hack -- it's probable that you'll need to fix a few bugs in the modules you use.
Overall I've been happy using node.js
