I don't know, I want to make an HTTP spider and I don't want to have one process per request, so the obvious thing was to use something asynchronous. Still, Python+gevent sounds better than node, so I don't see the advantages of using Javascript for that. What does it get me over Python+gevent, which has a more natural asynchronous programming syntax?
There are also threads, which are typically much easier to program for than an asynchronous system, but will still let you have more than 1 request per process.
I don't know, it seems that greenlets are basically exactly as easy to program with as threads, from a quick skim of the docs.