Paul Irish lead developer of Modernizr and HTML5Boilerplate and member of the jQuery team has two really great video tutorials about everybody’s favorite library up on his blog. If you haven’t seen them I highly recommend them to any frontend hacker.
He starts out how in the beginning jQuery (any library actually) is this black box that ‘just works’ and you have no idea how. He then explains some of the basic internals and also some of the more scary (and very smart) parts of the jQuery code. But what’s really cool is that the videos are actually very funny. The first video runs for about an hour and I never got bored watching it, in the contrary some of the things he does and says will just make you laugh out loud. And you’ll learn some impressive techniques that are actually quite useful in your day to day programming work.