Thankfully John Resig, Karl Sedburg and the others have steered slightly away from the profligacy of AJAX libraries doing the rounds at the moment and produced a library that actually deals with some of the problems you face as a web developer or a designer - namely things like clients saying "I'd really like the first paragraph after each header to be blue instead of black".
Now before I get shot down in a burst of "you can do that using classes in your p-tags" I'll say this - I don't want to, I shouldn't have to and it makes for ugly and unmaintainable code. Doing this just papers over the gaping holes left in CSS and makes your HTML even less semantic than it already is.
This is where jQuery comes in. The biggest area of development in this library has been in developing "content selectors" similar to the CSS selector specification. The brilliant thing about these selectors is that we don't have to wait until browsers with CSS 3 in them turn up before we can use them - thus saving us about 5-6 years of waiting time.
Watch this space as I think there will be a lot of development on this library over the next 12 months.
Source for citation: ajfisher.me/2007/08/25/jquery-saves-the-day.