Local High-school track is ideal for barefoot running. I have been running barefoot for the last 3 years. My knees don't hurt anymore. The ground up rubber surface provides a bit of cushioning.
What kind of track are you running on? If you tried that in the mid-west in the dead of summer on a rubberized track you would probably burn your feet and get blisters. My younger brother has tried it and experienced as much.