I bumped into Louis Stack last weekend on a hike up Moose Mountain (a 14 km hike with about 3,000 feet of elevation change), and he was wearing some crazy shoes that he was raving about. The hike is very rubbly in parts (see pic), and where I was wearing some mid-weight Scarpa hiking boots, he was wearing something called Vibram Five Fingers (which looked more like slippers with individual toes). I was surprised something so seemingly light and lacking in support could be used in such rough terrain. He commented about how well they work the muscles in the feet and legs, how natural they feel, and how they change the way you walk. It sounded very interesting and I could certainly understand how your muscles would fire a lot differently on rough terrain versus when they are supported in a hiking boot, and how you would develop greater stability and balance as a result. Louis always seems to at the forefront of new things.
(Here's Louis talking about them)