I was very disappointed to see that most of the book is made up of repeated source code examples. Parts of it is well written but it is very hard to get an overview and to me, it seems, this book was primarily made to make a bit of money while Ajax was still unknown and perplex. Although the authors give some fine examples of how to use the xml that Ajax is based on they don't care to explain how to expand your own knowledge and understanding beyond the simple examples they provide.
If you are satisfied with copying the source code shown in the book then this might be the book for you, but if you want to learn Ajax properly you should probably buy another book.
Also, it had the worst typography I have ever experienced, the pages looked as if they were printed from a cheap ink-printer!
I feel sorry for writing such a harsh review but there are so many parts that are missing. It could have been a good book with a little more effort.
I would be very careful about buying any books from this publisher.