The problem with the Earth Shoe theory is that your heel goes deeper into the sand because it is narrower and carries more weigh than the ball and toes, so the sand yields more it--

Walking in the sand actually causes your toes to bend up a bit, bending the instep uncomfortably upward and stretching the Achilles tendon and the Gastrocnemius muscle( are these names right, Mark?, it's been a long time..)--so if you spend a lot of time at the beach, you tend to walk on the ball of your foot rather than your heel--

Oddly enough, I think that those of us who tended to walk that way found Earth Shoes comfortable, because they gave us more room in the toes, and the low heel didn't bother us because, at least while we were walking around, we didn't put any weight on our heels--if you spent your time standing(instead of moving around), or walked "heel first" you were in for a lot of pain--