I'm disappointed in the lack of effort the authors did in compiling this book. They do seem to know the material, but the examples are largely just pages and pages of code that are not very well explained, and not very well tailored for a learning environment. For example, I consider Google's online tutorials excellent, such as this one here [...]
In contrast, the examples in this book are lazily put together. One of the key components to Google App Engine is the concept of Servlets. In this book, the authors dump 23 pages of code (pp 47 to 70), with tedious extraneous code, such as hundreds of irrelevant table styles (td bgcolor=#ffffff ). Not only that, but instead of just providing a single form element or two to make the point, the reader has to sift through pages of repetitive code doing the same thing for multiple extraneous elements. In the 23 pages, it is easy to miss the key critical things, such as how key elements are linked to other parts of the code. All that code could be reduced to a few pages to make the same points in a clear manner.
Unbelievably, they do the same thing in the next example explaining the Google Web Toolkit. Instead of just a one text element coded to enhance understanding, tons of extra code is devoted to coding repetitive elements, in this case, all seven days of the week are coded (with each 'day' element coded separately--taking up pages of code). It's clear they just dumped code from some sample projects instead of considering what would useful for teaching concepts.
Other "tutorials" such as how to link Flex, are copied from internet sources, but even more sparsely explained, and don't even seem to function, as another reviewer explained in terms of imported libraries. Often, a block of key code is shown, with no explanation of which file it should be part of (and Google App Engine requires coordination of a lot of different files). It's pretty obvious not a lot of effort was put into these sections.
Much better to understand the concepts of Google App Engine is the O'Reilly book, Programming Google App Engine. However, the O'Reilly book also lacks good tutorials.
Beginning Google App Engine does have some good information in it, specifically the introduction , but most of that information can be found online. I don't recommend this book.