This book contains lots of examples of how to use AJAX to perform a lot of the sorts of things that people typically use it for. If you just want to use Ajax the same way as everyone else whether your situation actually requires it or not then this may be the book for you. Personally, I would tend to leave and never return if a web site used one of the many inappropriate or US-centric scripts described in this book.
This is not a book for learning Ajax, it is a book for people who want to use Ajax without having to learn it. The book contains plenty of code samples that show you how to use Ajax to perform a number of tasks for which Ajax is the appropriate as well as lots of sample code to perform many tasks that are currently popularly performed via Ajax even though Ajax is not the appropriate technology to use. The book fails to distinguish when or why you should use or not use Ajax and just presents the how to use Ajax to perform tasks.
Probably due to the lack of equivalent non-USA services a lot of the scripts examples that show how to retrieve information from other sites are USA only in scope and so will not produce meaningful results for any visitors from the other 200+ countries. Unfortunately a lot of the scripts that don't rely on external services have also been provided with a USA only or mainly USA bias and so are also somewhat unfriendly to other visitors to your site.
I found the large number of inappropriate usages or USA-centric scripts in this book to be somewhat discouraging. Sure it would be possible to rewrite many of the scripts for use on the world wide web rather than the US web but most people capable of such a rewrite wouldn't need the information in this book in the first place.