Over at Smashing Magazine, Jon Bernbach wrote a nice article exploring cognitive load, "Ways To Avoid Overwhelming Users: Lessons Learned From My High-School Teachers".
There are two parts I especially liked:
First, he uses the metaphor of High School teachers to connect with the audience and demonstrate his point. Metaphors are extremely powerful ways to communicate abstract concepts, and there is no wrong way. If the metaphor you choose connects and communicates with your audience, then you've accomplished your mission.
Second, I like how he draws a distinction between intrinsic and extraneous cognitive load. Jon defines intrinsic cognitive load as "the complexity that is inherent in certain tasks or materials". Extraneous cognitive load refers to "superfluous elements" that are not necessary for the content.
Your ability to manage the user's cognitive load directly affects the usability of your interface. Jon's article is a good revisitation of cognitive load.