Google App Engine is great for those of you in search of a complete, scalable and affordable hosting solution. Especially if you start a project and you don't yet know exactly how successful it'll be (which mostly you never know), how much potential users you'll have and so on, then App Engine is great.
It allows you to start with a free plan and then to scale your pricing as the number of users and CPU resources increases. The advantage: you don't have to setup (and pay) for a huge system to cover the maximum possible work load, but instead just pay the exact work load you need.
So far one had to create the connection between client-side applications, whether from Android or GWT by hand (I know what I'm talking about). This means also to handle authentication issues and so on.
The video below - presented at Google IO 2011 - demonstrates the creation of a task management app with an AppEngine back-end (using the Google Datastore as persistence medium) and an Android as well as a GWT app as the client-side front-end. It nicely demonstrates a new template which an updated version of the Google Plugin creates with build-in authentication and Android to AppEngine RPC call mechanism.
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