The Barefoot Professor: by Nature Video

Obviously humans have not had running shoes since modern times, and regular shoes before the era of mass production were expensive anyway,so children regulary went barefoot due to the cobbler's fee.
But I wouldn't reccomend running in snow or cold surfaces unless you want frostbite nor on excessive prickly ground with huge spiky prickles without some protection.
As for the running shoes improving performance argument, clinical studies have made this claim seem shaky at best.

imagine steeping on crap

duh this is not new..........

On concrete? I think not!

Vibram Five Fingers are an excellent alternative to running barefoot, especially in the city.
Of course, running barefoot after a lifetime of running shod will take some getting used to and should be approached in phases until the feet are acclimated appropriately.
Any new physical endeavor should be taken cautiously. Just like when beginning weight lifting, you feel great until the next day when everything is sore because you overdid it - i.e. blisters on your feet :)

Yeah it would be really fun, running barefoot that is. It would be a ton of fun untill you run over a fking rock or nail.

Many people tend to forget that barefoot runners have eyes and are constantly scanning. If you have shoes on, obviously you're going to see this nail and avoid it. Same with barefooting.

Most standard running shoes wouldn't protect from nails jutting straight up anyway, which you are unlikely to encounter BTW, unless some has of course endeavored to booby trap the area you are running on.