I couldn't resist. Inspired by "Born to Run", a good story about ultramarathoning and the role of running in human evolution, I decided to try running barefoot. To protect my soles, I bought some remarkably silly-looking Five Finger Vibram slip-ons. They're like a removable callous, with a separate "finger" for each toe.
Bottom line: running barefoot slows you down and keeps you on your toes -- almost literally. You land on the middle of your foot, rather than the heel. And in case there's something painful under your foot that you didn't see, you must be ready at all times to take your weight quickly over to the other foot. You watch the trail much more closely. And since my weekend trail has at least one stream crossing, I don't have to worry about high water any more. The "shoes" shed water immediately. Minor worries: grass and small plants get caught between your toes; hitting a stone toe-on would be really painful; running on pavement is no fun at all; and the shoes themselves probably cause some callouses. Over all, though, quite nice. Light enough for a backpacking camp shoe, too, where the separate toes and flexibility will restore foot function after a day of tenderizing in hiking boots.