If you're hoping to hire people to use your chosen framework, Node.js might be a better choice than any of the ones you've listed.
Its not so much that there are more Node programmers than, say, Twisted programmers (although at this point there very well might be, especially in the Bay Area), but lots of people know Javascript, and both Javascript and Node itself are relatively easy to learn.
Edit: I don't mean to pick on Twisted here, I've been using it for about two years, and Node for only around two months, and I really like both.
I don't agree with this. If you're writing something that's http-only, then this might be true, since that's relatively easy (get data, push data). But if you write anything else, require custom protocols and thinking about state machines implementing specific behaviour with retries and reliable timeouts... "easy to learn" language, is the last thing you're worried about.
Why not? Using an easy language on a hard problem means you can hire someone who knows a lot about the problem instead of having to worry about the langauge. At least until the language starts getting in your way (and, in my limited experience, between Javascript and Node's Buffers, you won't find yourself too limited on protocol implementations).
This may be just my impression, but if someone really had a need for an async server, they wrote it in something else before. I'm not saying node.js is bad in any way, but there are more established alternatives in languages people already use. They were used before and they did the job. Is node.js going to be a temporary thing?... we'll see. Is it that different from what we already had? (compare http://github.com/jamwt/diesel/blob/master/examples/http.py and http://nodejs.org/api.html#synopsis-0 ) not really.
Its not so much that there are more Node programmers than, say, Twisted programmers (although at this point there very well might be, especially in the Bay Area), but lots of people know Javascript, and both Javascript and Node itself are relatively easy to learn.
Edit: I don't mean to pick on Twisted here, I've been using it for about two years, and Node for only around two months, and I really like both.