Shane's post reminds me of the wonderful lectures my art history professor at University of Oregon used to give. She would discuss how the famous artists intended to have the viewers eye move through the image and why and how all the classic masterpieces work the way they do.
This subject is important when you are attempting to create strong images. I think it helps to think about composition and what it takes to make a strong image. Some would claim there are rules of composition while others approach composition as a totally intuitive subject. Fact is there is probably a lot of both.
Shane's post goes a long way to get you thinking about composition. I can't say I agree with all of his conclusions or choices but the important thing is to start thinking about these issues.