A wonderful article filled with some awesome elements of design theory. There are entire books on the subject — but this does work as a decent primer to the subject matter. There are actually entire schools around studying this concept.

I’d probably suggest the following books for more on this subject

• Son of Web Pages that Suck
• Don’t Make Me Think

I uh… thought I had remembered more of these? Either way… good job on the quick primer that… actually has a LOT more material around it behind it.