I wonder how it might compare to Tornado (http://www.tornadoweb.org/)
Gevent uses the http server built into libevent, which is written in C, so it's no surprise that it is fast.
Eventlet (the project that Gevent forked from) allows you to write hubs while gevent only supports the libevent hub. So I made http://github.com/vishnevskiy/greentornado to allow Eventlet to run on Tornado's IOLoop. Been working for a while in production with no issues.
Would have made it for gevent though if I could since after reading the code of gevent and Eventlet I found that gevent's code base was much cleaner.
The Tornado people recommend running more instances of the application than CPUs to handle the short blocking requests to local databases and what not.
Although it depends on what your app does, my guess is that typical applications written with this philosophy are mostly synchronous code.
That being said we still use synchronous calls to our databases.