I just calculated that the amount of electricity needed to charge a "D" cell would cost around .2 cents. So you could charge five of them for about one penny. Lugging around batteries all the time to earn only a couple of cents per day wouldn't be worth the effort. I suppose if there was no electrical grid in the area, it might be a convenient way to recharge your cellphone or other devices.

I'm not sure how much energy can be put out by piezoelectric materials but it might be possible to embed LEDs in the shoes to light from the energy of walking so that a walker at night might be more visible in the dark. I know that reflective materials are used where a car's headlights could create reflective warning but LEDs would provide visibility where no other light exists. I have seen kids shoes with LEDs but I assume they might need batteries.

this whynot has some related links.

http://www.whynot.net/ideas/4735#comment-17418