As a professional farrier I have had friends, my mother, and clients touting barefoot trimming. One client point blank refused shoes for a toe crack, which was fine, they didn't show and had plenty of time to wait for a barefoot correction.
My concern about the "natural hoof" cult is that the horse is no longer a physically natural animal. After about 4 thousand years of human "improvement" we have distorted many breeds' genes so they simply do not grow sturdy feet. I do try whenever possible to keep a horse barefoot (mostly because I am lazy and don't care to go through the trouble of shoes unless absolutely necessary :P ).
As for mustangs (not an attack, I swear!), I do not desire a mustang's life for my horses, mustangs live hard and die young.
Just went to the barefoot website that was posted, sounds like the prescribed trim is exactly how I was trained to do it, so my experience with barefoot horses is still valid. Yay validity!
I do however strongly disagree with the idea of a fabricated "mustang roll". Unless the person performing the trim is absolutely 100% certain they are putting it in exactly the right spot for that horse, it can cause discomfort and potential damage to the knee. A horse's leg moves linearly, if the "mustang roll" (breakover point) is misplaced this will force the knee to bend at an angle not natural to that horse, causing lateral bending and breaks in the line of motion of the leg. I'd much rather just let the horse "grow" its own breakover point.