These comments (and the star rating) are very specifically from the point of view of someone who wants to add some interactivity and AJAX to web pages using the most straightforward efficient method, which is with JQuery.
THE BAD: Too few examples. Often complex commands are introduced without even an example to illustrate the syntax.
(FOR EXAMPLE, early on when selectors are discussed, they introduce a selector that requires quotes. That selector itself must be contained in quotes. They never show how the quotes within quotes syntax is handled).
In other places there is a surfeit of unnecessary technical material. The chapter on events, for example, starts off with long sections on the DOM event model and cross browser issues without a HINT that those issues aren't material to the JQuery user (that's the point! JQuery handles that stuff so I don't need to know).
Stylistically, these guys seem to be inspired either by ad copy (there is a ridiculous excess of exclamations!) or by programming blogs. They have the a fondness for jargon and dogma that seems to be the morass of the self-educated technophile. Many pages are wasted with examples of How HORRIBLE it was in the days before jQuery. In some sections (like the beginning of the AJAX section) they elaborate on the complexities of browser differences for AJAX calls. One of the most complicated sections in the book, only to show that you really don't need to know any of that stuff thanks to The Miracle of jQuery! (!))
Marginalizing that gift because of a distaste for the major browser (like it or not) just is not helpful. I'm not saying they deny the existence of IE. They just don't make it a focus at any point.
But in any event, the book should decide if it wants to be a reference, a tutorial, or both. I just think it's not a great introduction to a great subject. And I know it's a lousy reference, because I tried to go back to some chapters to look up syntax. Hard to find. Hard to read. And few examples.