Ben Dearman Barefoot Training: Running and Strength and Conditioning Interview
Some really good stuff there.
Flat footed people do tend to benefit the most from going barefoot because they no longer have that medial arch support to prevent their foot from crashing to the ground. Instead the muscles of the lower leg and foot have to control that motion now. And a foot that has proper motion, stability and mobility is a foot that is less likely to be injured with sprains.
(hat tip to Sprint Strong)