While I don't want to turn people away from this book, I would like to point out that many of the recipes in this book (like DOM manipulation, Ajax, styling, etc.) can be done more easily using a framework like jQuery. I suppose that is why I was somewhat disappointed by this book; most of the things it accomplishes can be solved using a few lines of jQuery.
I gave it five out of five stars for two reasons: First of all, it does provide some excellent examples, especially in departments where jQuery isn't all that useful like string manipulation and arrays. The date manipulation recipes are very useful as well. Secondly, I didn't think it was fair to give it anything lower just because I don't use all of the material in it. I'm sure that eventually I will end up doing some kind of raw DOM manipulation without jQuery, whether it be with Greasemonkey userscripts or on portable devices, or for very short scripts.
In my opinion, this book is for someone who is not using jQuery (either because they don't want to or can't) or for someone who is developing a JavaScript framework. I would also recommend it for anyone who wants easy-to-use examples of array, string, and date manipulation.