I don't know how everyone feels on this subject. Some feel it is an invasion of privacy, however considering the fact that you appear on film multiple times each day unknowingly. Well in the US and the UK anyway. CCTV, Traffic Cams, Store Surveillance, etc. I would suggest strongly that you look into local privacy laws regarding photography in your area, before undertaking this genre of photography.
Me, I love it because you catch raw emotion. People aren't saying "CHEESE" and it's not some model pretending. Here are a few I've taken. Now these are altered. I'll explain I turned them B/W, because I think it make photos more dramatic. I also added a sleight HDR effect to some. I thought it made them look more interesting.
They were to big for me to post the regular way.