Comment JQuery is the JavaScript Standard library. (Score 2) 126
In my perception jQuery has basically become the JavaScript standard library.
Basically any combination of frontend toolkits has it included somewhere, so you don't even have to worry about doing that. It's the default for Joomla and Wordpress and there are a measurable amount of functions that take care of the gruntwork and normalize utility across browsers.
On top of that, the amount of JS projects relying on jQuery as a foundation is staggering. The secondary market has tools built around the jQuery ecosystem and the project as a whole does an excellent job at marketing and advocating.
I personally see the next generation in such avantgarde stuff as Googles Polymer (pretty amazing) but until everyone has moved to SPAs and web components - which is not happening any time soon - but until then it's not the worst idea to familiarize yourself with the concepts and the utility funcitons of jQuery.
My 2 cents.