A pretty good book, with some decent examples. Unfortunately, like, half the book is boilerplate text ("here's the code, type it into a text editor like Notepad, ya-da-ya-da"). I'd prefer they include less boilerplate and more examples.
Other than that, not bad. It's certainly helping me get a grasp on jQuery. Worth perhaps $5 if you find it used, and you're a jQuery-newbie like I am.