I learned a very valuable lesson on Friday - don't run barefoot on a real trail. It hurts. A lot.
I suffered through 2.5km before I decided to give it up. I turned around and walked back to the beginning of the trail, so I really spent 5km on serious rocky trail, though only about 2.5km were running.
When I got back to the road, I figured I would run along the road for a bit until the group finished the trail. My feet were so sore I could hardly run. Now it is Saturday night and they are a bit better, but still sore.