This is the second book about ajax that I have read. And what a book it is. If you want to go into the depth of ajax this is the book you want. Within this review I will explain why.
This book is devided into four parts: Rethinking the web application
Discusse the more advanced Professional ajax side. Now we are learning about security, usability and performance. Also very interesting stuff Ajax by example
Interesting if you want to learn how it really works, I'dd rather use an existing library, but it is fun to learn.
So this is a great book, with real live examples and a very wide coverage of the subject.