Last spring 2009, we attended an American Society of Mechanical Engineers (ASME) meeting, and the featured speaker described graduate school engineering projects involving ENERGY HARVESTING - the capture, storage, and use of energy from motions, etc. The only example I can remember right now involved devices on bridges which generated and stored electricity due to the motions caused by the wind. When I glanced at the shoe designs involving such devices, I thought: "That's an interesting idea..." One final comment, my favorite Christmas present last year was an old-fashioned, mechanical watch, which is SELF WINDING due to the motions of my arm. In this case mechanical energy is stored in a spring. Let's all think GREEN and look for these "virtually free energy sources."