When I was a kid in rural PA, I basically never wore shoes - other than to school, church, shopping - from late March or early April until late October/early November.... and by mid-April or so I could run barefoot on a gravel drive or negotiate a multiflora rosa thicket (I had a "fort" in the middle of one).
As an adult, I kept doing that as much as possible, but never got my feet quite THAT tough again. In the last few years, though, I've not had the time to harden off my feet in the spring.
I used to get some VERY weird reactions from people at the park mentioned up-thread, btw, since you get a lot of citified types in the "park park" area of it; I swear some of them had never seen a person without shoes.
Heh, well... *I* ain't the one worried about it. My S.O. grew up on 12 rural acres, and returned to them a few years ago - but he was always forbidden to go barefoot because of "getting worms", hence the ongoing debate about whether or not I'm risking my health when I weed the garden etc. sans shoes. I need to bestir myself and find some factual ammunition before next spring.