Here's an interesting example of a mobile exergame. Arukotch is a tamagotchi-like virtual pet embedded in a pedometer. The "pet" is a "shy girl waiting for a proposal from a cute boy." The more steps you take, the more "healthy and beautiful" she becomes. Items like cell phones and gifts also reveal themselves as you walk more. These items can aid in obtaining, you know, a cute boy.

Arukotch has been around for a few years, although I can't tell if it's still being produced. The concept is sort of insipid, but the coupling of movement to gameplay is more interesting than more complex and gimmicky physical controller. I do wonder which sort of physical games are capable of producing more results, little, cheap, low-commitment temporary ones like this one or large, expensive, ongoing ones like Wii Fit.

(thanks to Julian)