In either case during my preparation for the 2004 NYC Marathon I would occasionally find myself stepping out for a run unshod. As I was living in Boston at the time, running the streets and sidewalks sans-soles was not terribly appealing since the sidewalks often had glass or other less pleasnat material on them. In fact, it was a disgusting idea. So I would trot over to a nearby track and do laps on the grass. The onset of cold weather followed by an extended break from running after the mearathon meant I didn't pick it up again for some time.
At graduate school running was my great escape and I would slip back into barefoot running whenever it rained. A lap around campus on wet concrete and grass was both more exhilirating and relaxing than any other escape I could conceive.
When I moved to Boulder I continue my shoeless jaunts in the rain, though these were fewer in Boulder's dry climate. They were also still almost always quite short, largely because I was self-conscious about it. It attracted odd looks, even in Boulder.
Lately, though, I've been doing it more. In part because I started running in Vibrams and in part because I miss the sensation of the earth/grass/road on my feet. I enjoy feeling more connected to the environment around me and the sensation of nimble-footedness that you cannot get in any pair of running shoes. And really, isn't enjoying it what it's all about?