Reading an article in the Journal of Cleaner Production on Human Powered Energy Systems. Three case studies were: mp3 player, auto-closing door, and electronic auto door opener.
The mp3 player and door had a lower environmental impact. The auto keyless entry device was about equal environmentally, but thought to be more reliable. The mp3 player required 1 minute of human charging for 60 minutes of run time.
Perhaps human powered devices can/will spread to non-vehicles. We've all seen some specialty devices for camping. Some have auto charging (kinetic) watches. Wouldn't it be neat to get the majority of little consumer devices to drop the wall chargers?