If you want your walking workouts to count, download the free Charity Miles app for iPhone and Adroid, select a charity, and start the timer when you go out for a walk, run, or bike. Walkers and runners earn 25 cents per mile and bikers earn 10 cents per mile for their chosen charity.
Too good to be true? No, it's the real deal, up to the initial $1 million provided by sponsors. And part of the deal is that after each workout, you must post it to your Facebook profile to spread the word in order to "accept sponsorship." The charities to select from are limited, but growing. The developers believe that as the user base grows, so will the sponsorship money and the choices for charities.
Currently, it uses your phone GPS, so it won't work indoors on a treadmill or exercise bike. It's not a great exercise app, you get a total mileage and time at the end and can see daily totals. It doesn't integrate maps, etc. But I can run it at the same time as apps that do that, and meanwhile be earning money for charity.