I would like to develop a web-app requiring data persistence using GWT and GAE. As I understand it, my only (or at least by far the most convenient) option for data persiste
I believe Google's official answer for this is GWT 2.1 RequestFactory. Given that you are using GWT and GAE, I'd suggest you stick to the official Google framework... I have a similar GWT / GAE based app and that's what I am doing.
By the way, setting up RequestFactory is a bit of pain in the ass. The current Eclipse plug-in doesn't include all the jars but I was able to find the help I needed, in Stackoverflow