The problem with this book is that it jumps around a lot and I mean a lot. All the topics are in there, but not in a logical progression. If I had not needed this as a required text for a class I would not have bought it.

Basically this book will hardly teach you anything you don't already know. They assume prior knowledge about almost every single topic they cover. They say in the preface that this book is not about java-script DOM, XML, AJAX or any specific technology for that matter. This book is more like some overview of all the technoligies that are used in Web 2.0 sites but none of them are explained in a way that someone without prior knowledge would understand. This book may only be useful for you if you are an experienced web developer with thorough knowledge in both backend and frontend technologies and just looking for some better practices and tips.
Unfortunately there aren't so many people that fit that description.