I liked this book. First, it is comprehensive in its coverage. It hits upon all the standard user interface functionality for which one uses jQuery: menus, tabs, slideshows, animated effects, using AJAX to update only part of a page, and so on. And these topics are thoroughly presented: they are always accompanied by useful code examples, along with detailed analysis of the code.
Another thing I liked is that the book provides oodles of references to the more popular jQuery plugins and User Interface Library components, which can make creating the above-mentioned functionality even easier. It's a great list of resources that's very practical in helping you to get things done without reinventing the wheel, and again, the authors comment on when plugin use is or isn't suitable.
One more thing in the plus column is the authors' enthusiastic, lighthearted style in presenting what's often rather dry material. The sample website used throughout the book, for example, is a parody (I hope) of all those sleazy celebrity gossip websites so prevalent in our current culture.
Speaking of daunting, a small criticism would be that the chapters are a tad too long for my taste, and even with the humor can be slow going. For example, Chapter 6, "Construction, Ajax, and Interactivity" came in at about 50 pages, and it seems that the "Construction" section, which contains the "best practices" just mentioned, could have been broken out into a separate chapter. Other chapters could have benefited from the same kind of treatment, making them more approachable – and making information more findable later.
All in all, this book does a very good job: It provides a comprehensive, sound, and practical treatment of jQuery, with plenty of examples for putting it to work in real-world situations, and it can be a valuable resource for both jQuery novices and more experienced developers.