If you're still mystified about the ins and outs of HD content and hardware, or know someone who is, we were both surprised and impressed by this semi-snarky PDF coloring book on the topic (which we first saw on The Consumerist).
Despite the ironic hipster tone (the narrator is a hippo in a dress), there's actually some good, simplified information in the project--created by the guy behind the kids' product review blog NonToxicReviews.com.
Heidi, the HD Hippo, explains the difference between SD and HD, asking readers to, "Take your crayon and draw 480 dots inside this TV, [then] take a different crayon and draw 1,080 dots inside this HDTV." We'd nitpick about the importance of plasma burn-in, but for a satire, the coloring book does a decent job of explaining the basic concepts behind topics like DLP projectors and upconverting DVD players.
If you haven't gotten enough, Heidi closes by saying, "In the future we'll learn about digital right management, fiber optics, HDCP, and regional encoding!"