I run barefoot about once or twice a week. I'd always heard that running barefoot was really bad for your feet and that you would really hurt yourself by losing the shoes. Hearing that always made me wonder how armies of old survived without Nike and Adidas to supply them with running shoes. So, based upon completely anecdotal evidence and my experiences going barefoot as a child, I decided to work barefoot running into my exercise routine.
I don't run on hard surfaces (with the exception of one Halloween night when I ran 4.5 miles on a sidewalk back to my apartment, while drunk) and I don't run on sand, and I've never had a problem going barefoot at all. I typically only do short runs (three miles max) barefoot, and I worked up to them very gradually. In order to deal with glass and other sharp objects, I use my eyes. (I've had tons of people ask me how I don't cut my feet when I run barefoot... I WATCH WHERE I STEP. Duh.)
Anyways, I haven't had a problem going barefoot and I am pretty sure my feet are a lot stronger since I've started going barefoot. My soles are a lot tougher now also. If you do go barefoot, I recommend running on a nice grass field or on a packed dirt path. Someone once told me never to run barefoot on sand because your arches aren't designed to take impact. I've tried running barefoot at the beach once or twice, and it makes my feet and legs hurt, so I don't do it.