I've been working for some time on a sample application with a Flex client and a Google App Engine service. It is based on a PureMVC example, but with many modifications.
This sample application is able to show, create, edit and delete projects and also project participants.
Although I still plan to improve it to learn about other approaches, it is already working and maybe it can help others learn about PureMVC, Flex, Python, GAE or PyAMF.
The source code is hosted on github:http://github.com/fernandoacorreia/flex-and-python-test
I've also been publishing several articles describing the approach I am taking:http://fernandoacorreia.wordpress.com/
I hope this helps. Feedback is welcome.