I've gone barefoot many times in the NY subway. I met two girls who also went barefoot, another put on sandals and said she wouldn't go barefoot down there. At one Dead concert at Madison Square Garden I met 3 girls. Two were barefoot with filthy feet, the other wore sneakers because she "didn't want to get her feet cut up." We all took the train down to West 4th Street. Three of us barefoot, the other shod. This was all quite a while ago. I haven't seen anyone barefoot in the subway, or streets, in years
A friend of mine goes barefoot on the London underground all the time, as i do when i'm down there. On my last visit 3 weeks ago, a girl asked us why we weren't wearing shoes, so we told her...
I always go barefoot on the train. It feels more comfortable and looks better than being in shoes. My feet do get very dirty though!