I just don't see jQuery as a grand interconnected topic deserving of "book treatment." It shouldn't be seen as something that requires one to read a book before you can start using it. Just find the function that does what you want to do in the docs, read the description and example code, and use it. Before long, you'll intuitively get the jQuery aesthetic. There is no reason to try to master the theory before attempting to actually use jQuery. There is no theory. It's all very simple.
Now, on the other hand, if you don't yet know Javascript and you're trying to use jQuery, I would suggest learning the syntax and semantics of the language first. But if you know Javascript, then jQuery is trivial.
In that respect, I think maybe the biggest value in this book is the Javascript overview at the beginning. Too many people try to use jQuery without grasping its foundation.
Just find the function that does what you want to do in the docs
I often go looking for the wrong thing. I'll think "In Ruby/plain JavaScript/C/whatever, I'd achieve X by doing Y and then Z" and then look for jQuery's equivalents to Y and Z, rather than doing it the easier and conventional jQuery way.
Books are good at relaying the thought processes of experts rather than the function by function material that, yes, a reference site provides a lot better.
For a slightly convoluted example, let's say I have a little JavaScript and DOM knowledge and am a few days into using jQuery without following any serious tutorials or books. To change the code within an element I might try something like $('#whatever').innerHTML = 'whatever' rather than the more jQueryesque $('whatever').html('whatever') - a simple example but it can get a lot more elaborate than that.
However, it's definitely a case of different strokes for different folks. You might be able to pick up on the idioms and nuances of new libraries and languages without much guidance, but books like Rebecca's can provide a much needed "guided tour" for some people nonetheless.
All of the above is why I wrote Beginning Ruby despite the existence of the venerable Pickaxe. The Pickaxe is an awesome reference book with a relatively weak tutorialesque set of chapters tacked on the front. My book caters to people who want to learn in a more linear, narrative fashion (and, to be fair, has a relatively weak reference section tacked on the end ;-))
Reiterating what petercooper said: if learning by book isn't your cup of tea, don't do it. On the other hand, lots of people find books helpful. Additionally, while plenty of people may find benefit in this document as a book used for self-led learning, my real goal with it was to release material that can be used for teaching. In that scenario, the people reading it have already expressed some interest in learning jQuery with the help of someone else, rather than just reading the docs.
I'm an okay jQuery/Javascript developer who gets stuff done - by going the way you said - search the docs for the function that I need.
I learned a lot of bad habits this way - because there are always two (or more) ways of doing things, and one of them is usually better than the rest. I just figured out that I was doing those things wrong when reading the book.
When I started learning jQuery, I scratched my head over this issue - I assign event handlers for a class, but they don't apply for elements that were added later to the DOM. Had the aha! moment when I figured out what was happening. The best solution I could find was to keep on assigning the event handlers whenever I added something to the DOM.
It served me well but Rebecca just taught me that there is something called $.fn.live and $.fn.delegate designed solve exactly this problem. This I would not have searched in the docs because I did'nt know that there existed something to solve this; and even if I thought there did, I might not have been able to frame the right question.
And there are lots of other gems that I picked up from this book.. jQuery really needs this. Especially for beginning developers who discover the power of jQuery - it helps them learn the right habits from the get go.
And the book is very concise and informative that the author deserves great praise for an excellent job.
Now, on the other hand, if you don't yet know Javascript and you're trying to use jQuery, I would suggest learning the syntax and semantics of the language first. But if you know Javascript, then jQuery is trivial.
In that respect, I think maybe the biggest value in this book is the Javascript overview at the beginning. Too many people try to use jQuery without grasping its foundation.