Here is a little news for Google App Engine developers:
Over the summer, I've been asked to review the draft of the book Google App Engine Java and GWT Application Development. Even with my experience, I learn few techniques, like with the object relationships (chapter 5). A very good book for beginners/intermediates, and still an interesting book for experts.
Note: I've no incentive to sell the book, just the pleasure to share a good reference ;)