I somewhat disagree about documentation...with regard to jQuery library itself. A few years ago I looked at the major libraries, Mootools , Prototype, Dojo and jQuery wanting to start learning how to use javascript. I had no background in any programming language except for some HTML and CSS.
I chose to learn how to use jQuery simply because the API documentation was the best. I never bought a single book and self taught myself how to use jQuery by following the forum ( was originally a Google group). By using problems that others posted as sandbox trials, and using them to extend my knowledge of various aspects of the API I was able to quickly expand my capabilities. Many of the sandbox attempts on other peoples problems in the early stages would not be entirely succssful or would be very inefficient code or would be completely over my head, however the solutions that others with greater knowledge would provide would trigger a bell..."so that's how you do that".
As time went on and I encountered something in a project I needed to implement but had never done, often I would have seen something similar posted in the forum, go back to the thread and use it as foundation to implement what I needed...and raise my skills another notch. jQuery doesn't cover javascript needed for things like string manipulation, date, regex , math etc. Again...I started jQuery with no javascript background at all... so I would use online resources ( mostly w3shools) to back and fill my knowledge on native javascript as I needed.
As a result of what I learned, much of it gained from following the forum, I am now able to build feature rich interactive ajax applications.
Because I learned so much from this forum, and it has been my primary learning tool, I now try to give back as much as possible and am able to respond to the majority of the issues that are posted here daily.
This forum is the second best jQuery learning resource there is! The most important is the API, filled with examples for each and every method...I still refer to the API often, many times to provide support links for others, but also to validate my own code
One other tool that helped a lot was a jQuery cheatsheet but that was before the API site was restructured with autofilters to quickly isolate methods.
If you really want to learn jQuery, save your money and follow the forum... pick a few issues here and there to try yourself, then look at the solutions that others post to the same issue and you'll be flying in no time