I mean not totally barefoot, I mean using VFF or something like Nike free run 3.0, in my long run I do a good 10-13k in barefoot, but after that my feets gets a lot of pain. I think my foots has been much stronger, and maybe it could be a good distance to run just 10k barefoot for maintaining stronger feets, and then to do long run with a cushioner shoe..
Edited: My Body weight is 83k, and my height is 1.80, I think running barefoot could be maybe something for people that weights <= 70 Kg on long distances, but for heavier people we must do just 10k or use maybe a middle cushion shoe like Saucony Kinvara 3 that alows you to run like a forefoot strike runner but alows you to run heel-strike too.