A straight forward introduction to Google App Engine architecture by Kevin Gibbs at Campfire One (April 7, 2008).
App Engine also includes the Django web application framework, version 0.96.1. Note that the App Engine datastore is not a relational database, which is required by some Django components.
I don't yet write python but I love have a dekho at Google App Engine soon.
The transcript of the talk is also available.