This book is a revised and updated version of an earlier version of the book. I would start off by saying that if anyone wants to learn jQuery from the roots up to a level of decent expertise, go for this book, it would be worth every penny spent. Thats how much I liked this book. The book starts from the very basics starting with simple examples and progresses with each chapter into more complex and real world examples with a step by step explanation of the code. You cant ask for more than that, really.
The book is based on the latest version of jQuery (1.3) which is why it includes the new .live() and .die() events. These two events are pretty magical, as they can bind or unbind event handlers to objects that get created on the fly as well. So, if you have a link within a div with a click handler on it, it would work but only on that link. Any new links you add dynamically (e.g. loading rss feeds etc via AJAX) wont have the event listeners attached to them. With the .live() event, you can do that . I find in pretty magical!
The book also goes at length to explain the plugin architecture and the best practices to write universally consumable plugins without breaking or interrupting any other user defined or plugin defined code. Infact, it also lists the most widely known plugins in the jQuery world in one of the chapters. There is a whole chapter on plugins!