I was thinking of putting up some “how to” articles on basic photography and found that someone had already done it. From Richard Burke and eHow – How to use the Rule of Thirds in photo composition:
The rule of thirds has its origins in classic Greek philosophy. They discovered that things appear more pleasing visually when presented in certain ways. Applied to photography, the top horizontal line is called the “eye line” and the lower horizontal line is called the “horizon line.” In a portrait photograph the eyes of the subject would be on the eye line and in a landscape the horizon would be on the horizon line. The rule also suggests that picture elements should be at the intersection points of the center square. Of course, there is a whole school of photography that believes that a subject should never be in the dead center square. In my opinion, the whole principle of the rule of thirds should be to get the photographer to ask one key question: “What am I taking a picture of?” Ask this question first and then compose your picture considering the Rule of Thirds. It is a rule, not a law.