Totally cool, but longish, video on the history of the wah pedal. Definitely worth the time to watch.
Best line in the video: Charles Pitts talking about working with Issac Hayes on "Shaft" and only staying on the G for the entire song until the very last phrase: "To me it seemed repetitious, redundant, and ridiculous. It shows you what you know." (27:52 or so). Just goes to show you that you never know where something will take you.