Also don't forget cogen, a library for network oriented, coroutine based programming using the enhanced generators from python 2.5. I recently used it as a front-end concurrent WSGI server in my Google Summer of Code project.

Besides state machine simulation, corotine has many other usages as well (eg. implement concurrency), it is a very powerful tool that not many programmers know. For those who are interested, I suggest a tutorial:

http://www.dabeaz.com/coroutines/