Tekuteku Angel Pocket allows you to walk with a reward in the works. The Japanese have invented a game that is powered by your movements.
Hudson Soft has the cute little pedometer that will track your walking progress and then you can upload your figures to your DS to monitor your caloric output and general health readings.
The little figure on the pedometer slowly loses weight in the picture as well. The graphics snhow you evidence of that reward for walking. Encouragement or otherwise, this sounds like a wonderful start to healthy choices via technology.