This review pertains to the Kindle Edition.
So, I really welcomed and valued the first 2/3 (or so) of Flanagan's book (or chapter), which is a narrative description of the library's features, with examples and detailed explanations of what's going on behind the scenes. Writing that sort of narrative about a programming language is hard, and Flanagan's only peer for that, in my opinion, is Friedl of Mastering Regular Expressions (also an O'Reilly book), and he succeeded here well enough that a person can actually read the whole thing with considerable understanding, thereby gaining a better overview of the library than can be had by searching out features when we bump up against something we don't know how to do. The last 1/3 of the book is a reference section: concise, simple, and well-organized, just what you need when you forget a particular syntax.
The book was carefully adapted to electronic viewing. Code is displayed in a fixed space font to differentiate it from the surrounding text, but the font has the same height and color as the text and so is easy to read. Sidebars are presented with a slightly smaller, but still easily readable font, as a distinct block of text embedded with the main text. This, and the larger work from which it was extracted, are the best examples of technical books adapted to e-readers I have seen, so O'Reilly deserves considerable credit for their success in this format.
The book was written for jQuery version 1.4 and the current version is 1.6.1 (as of today), and quite a bit has been added to jQuery. I knew that before I bought the book and decided the reference retained enough value to be worthwhile even though the version had been superseded. You should bear that in mind, though.