I hike with little cushioning quite a bit.
When I did the Cactus to Clouds (climbing San Jacinto from the desert floor and then doing a big loop) trip with Nick Gatel, we both wore XC racing flats.
I had on New Balance MT100s that had at least 350 miles on them (read: bottomed out) and no insoles. Nick wore a pair of Saucony Shay XCs, probably a bit more minimal than the MT100s.
That was a ~60 mile mile trip with over 20,000 feet of cumulative elevation. We did it in 2 nights and 2 1/2 days.
I did the first ~10 miles without socks.
That trail hit everything- hot and dusty hardpack, snow, forest duff, and plenty of rocky sections and we both did great.
At some point Nick did develop a blister sort of thing from kicking/stepping on a sharp rock. Not a friction blister, but real deep under several layers of skin between his big toe and foot (if I remember correctly). Perhaps this could have been avoided with thicker shoes? Nick toughed out the injury like a true champ, but I could tell it was bugging him. He must have done ~30 miles with it. Seems to me it was more of a bad luck injury that likely could have happened regardless. I'm not sure if he's changed his verdict on his XCs since then.
Regardless, I think we both felt the minimal shoes were great. While there might be a greater chance for impact injuries, I think they lessen the chance of rolling an ankle, slipping, tripping, etc.
I'm sure it's something that takes getting used to, working into it slowly. Roger is certainly right though- prolonged rocky, rough surfaces get pretty exhausting. I currently have a slightly bruised sole from a rock, but it doesn't change my opinion on shoes; injuries occur wearing anything. Overall, I feel flat, less padded shoes (especially with little heel lift) are safer due to better grip (more feel) and stability.
I've also done some trips in Five Fingers but don't like them. Lack of cushioning isn't the issue, it's the lack of insulation from the hot ground combined with a glove-like sole that gives no room for air and no breathability.
When I get a little money to spare for goofing around, I'll be buying some Vibram rubber for homemade huaraches. Not sure they'd go on a long trail with me, but they certainly seem fine for shorter trips.