I agree that these shoes are fantastic for running. The one thing that annoys me about them though, are the independent toes. Sure, they feel a bit more "free" than normal shoes, but on the other hand, they make the shoe tougher to put on, require expensive toe socks, and make it easier to stub toes.
Not exactly an answer to why but the individual toe pockets can also help you if you have a neuroma since they spread out your toes a bit. I know a few folks with a neuroma that swear by these shoes.
I wear mine without socks; the chafing you'd get with normal shoes that way is completely absent if the Vibrams are correctly fitted, and they have a somewhat-effective antibacterial coating.
