As can be inferred from the title, the book is meant as reference. Don't expect to learn fundamentals of jQuery by reading it. It's better to pick up some other title (jQuery in Action, Learning jQuery 1.3) for that purpose. The book does, however, excellent work at providing solid examples of each function jQuery provides. It is important to note that the reference does not cover jQuery UI! In addition to function reference the book provides a look at the plugin architecture of jQuery.
Analysis
I found the presentation of the book nice. There is just enough detail to figure out how some particular function happens to work. Should I need to check something out I'm sure to use the book before looking at the online reference. It's that handy.Of course the problem with this kind of books is that they get outdated within a few years but I guess it will do more than fine for now. Even though jQuery advances quite fast it seems the fundamental ideas are pretty solid. It's just a few functions or so that might appear in the library. Lately the development team has widened its focus to mobile platforms. Personally I find that great.
You can get a better idea of what the presentation of the book looks like by checking out the free sample chapter. You might find table of contents handy as well.