At AudioBox (https://audiobox.fm)
we have a strong use case for it.
We are already providing our users a "live filesystem" with Box, exciting that Dropbox is also adding this.
Domains are 0.10 specific I believe, and 0.10 is still bugged in few areas. I'd stay on 0.8.23 for quite some time since we are talking about stability.
It works for us, but it comes with a lot of issues, some of which are pretty major, although this holds more true in the ecosystem, not always in core.
Problem is see is that no one seems to know how to solve them (it's a callback, no it's node, no it's v8), takes so much time or just plain don't care (socket.io, I'm looking at you), so you're on your own if you encounter something critical.
Either case start getting traction, don't over optimize at the start and watch out for memory leaks: there are tiny bits of best practices that you must follow (always consume the response? check. close the request appropriately? check. don't crash the whole node process? check.), some of which not really well documented, that can ruin your day should you get some important press and are not implemented correctly.
Take a look at the issue tracker of the libraries you are going to use, check if there's something that can affect you and perhaps contribute back!
We'll have a look at this after our next release.