Now, I've been using JQuery for some time now...and have absolutely fell in love with it. The ease and elegance of adding functionality with the library is simply amazing. Also, since JQuery is only one file (yea, that's right) its very lightweight, its extremely fast, and very robust...and its being used all over the web in some of the most famous websites out there.
The JQuery API and the simple selector style of getting and manipulating DOM elements makes it incredibly easy to use. The API allows you to string or chain together commands -- to make one command feed into another, allowing you to build effects and functionality on top of each other.
The selectors used to obtain elements are based on a combination of simple CSS and XPath styles, so anyone with CSS knowledge should have no problem with using the library.
Check out some of the cool functionality you can add to your websites:http://www.noupe.com/jquery/50-amazing-jquery-examples-part1.html
And here are 51 of the best tutorials you can use to get started:http://www.noupe.com/tutorial/51-best-of-jquery-tutorials-and-examples.html
And if you havent noticed, CodeAsp.Net is using JQuery through the community. You'll see it in action on the homepage in the "Whats New" section with the tabs... and the "Top Members" uses a JQuery carousel approach.