[stephenyoung]

Definitely. Not to the extent that you've basically in your mind got every piece of jQuery mapped out, but you should at least build the ability to jump into the source code and see what is going on, and know the base concepts. For the same reason it is advocated to learn C but develop in something higher level - you need to know what pointers and memory management are to adequately grasp why the things you are developing are reacting in certain ways. I generally crack open the source code whether or not I'm having troubles, I think seeing and dealing with other people's code is one of the most beneficial (and humbling) habits a developer can have.