My jQuery level was pretty close before I took the time to read this book. I’ve found this book amazing and really interesting even for fast-learner as I am (knowing dozens of languages and libraries I tend to go really fast when I’m studying a new language or library). I think this book is mainly for beginner or intermediate users since it focuses the reader on the main parts of jQuery UI leaving aside some real-world and advanced coding details that may be crucial in the real world development.
A thing that I really like is the approach “one widget = one chapter”. In this way you can jump straight to the chapter that you need without having to read more that 200 pages that you don’t care about, in that moment.
The book comes without Index and this is sad, I think. Even if in this kind of book is not necessary, I think that is a very cheap feature that all books should have.
I would recommend this book to everyone is a jQuery and/or a jQuery UI novice or beginner user. If you are already an advanced user you may want looking toward something more hardcore.