You were designed barefoot.
Went for a two-mile run today in my FiveFingers, and felt great. It's basically running barefoot. No arch support, no shock absorption, no heel cushion.
Isn't that dangerous? Very - if you run like your shoes have allowed you to. But we were designed to run on the balls of our feet, without a heel strike. Shoes protect your feet, but they let your form get sloppy, with lots of heel strike and almost no use of the muscles in your feet and lower calf. Weakening of muscles there may cause more injuries than the shoes prevent, because the exoskeleton of a shoe cannot be as strong as the internal skeleton and muscles of your feet, if those muscles are allowed to develop.
Running barefoot forces you to run on the balls of your feet. It's smooth, efficient, and good for you. Your feet and lower calves may be sore, but that's because you've never used those muscles before.
And strengthening those muscles improves balance and agility and can prevent injury.
See this article for more detailed and study-based information.