It is a wholly interesting read, and you should really check it out over at 1UP. Among assorted anecdotes about demo controllers almost being thrown in anger (what?) and how the Playstation console was a box with a circle in it comes the reasoning behind those symbols that make Xbox and Nintendo gamers scratch their heads:
Other game companies at the time assigned alphabet letters or colors to the buttons. We wanted something simple to remember, which is why we went with icons or symbols, and I came up with the triangle-circle-X-square combination immediately afterward. I gave each symbol a meaning and a color. The triangle refers to viewpoint; I had it represent one's head or direction and made it green. Square refers to a piece of paper; I had it represent menus or documents and made it pink. The circle and X represent 'yes' or 'no' decision-making and I made them red and blue respectively. People thought those colors were mixed up, and I had to reinforce to management that that's what I wanted.While I understand the Japanese see circles to mean "yes" and Xs to mean "no," the western gamer will always want the button under their thumb to mean yes. We're impatient, you see?