I agree with what all have said, but I may be a bit biased. I feel that unless a horse NEEDS shoes or if they're being ridden on the road, they should be barefoot. My mini reasons for that is when a horse steps, everything is absorbed and felt by their frog. That's what keeps their blood flowing through their legs. When you put a shoe on a horse, the frog doesn't touch the ground. The result - the horse's legs feel like pins and needles all the time, like when your leg is asleep.
That's just my little spiel, haha. I'm just a firm believer in doing most things with horses the 'natural' way, but as I said above, if a horse needs to be shod, they should be all means be in order to keep their hooves and legs healthy.