Concurrency in Python

Using Coroutines to Create Efficient, High-Concurrency Web Applications
In this talk Matt Spitz evaluates several ways to deploy WSGI applications. At Meebo, they settled on gunicorn + gevent, preferring it to mod_wsdi and Twisted.

PyCon 2011: An outsider’s look at co-routines.
This is an overview by Peter Portante that compares greenlet-based approaches like gevent with yield-based coroutines and threads.