If you have the money and inclination to buy all but one of O'Reilly's definitive guides then this is the one to leave out.
In reading this book I started to wonder whether it was written in 2008 or in 2002. Certainly the earlier date seems more plausible given that the author seems to spend a lot of time concerned with browsers which were popular back then but which were soon after declared officially dead and buried. A lot of the coding techniques for the client side processing also dates to about the same era and wouldn't be used in a more modern web design.
While this book covers many different aspects of Ajax rather thoroughly, the suggestions made in many instances demonstrate a lack of knowledge on the part of the author.