Check out what they're doing at the Paris marathon this weekend...

Paris Marathon organizers will lay energy-harvesting tiles across the course on Sunday to ensure not all the effort expended by the race’s 40,000 runners goes to waste.

The flexible tiles made from recycled truck tires will span a portion of the Champs Elysees for about 25 meters (82 feet) of the 42.2-kilometer course, according to Pavegen Systems Ltd., the U.K. maker of the tiles. Each footstep generates as much as 8 watts of kinetic energy, which is fed back to batteries that can charge display screens and electronic signs along the route, the company said.
— Paris Marathon to Harvest Runners’ Energy With Pavegen Tiles - Businessweek

What a brilliant idea and definitely something I think should be deployed more often, and not just in road races, everyday life too. Anywhere you have moving traffic of any source is potentially a location to harvest energy.