For the sake of defining it, one might say Street Photography is a still documentary of our times - life as we know it or see it. For many it is a mirror to the society, while for some it is a reflection of the photographer’s thoughts, portrayed through the events of real life. However there is no fixed definition. It is open to interpretation, open to experimentation. In the course of time, I have been asked a number of times about the ethics of it all. Street photography is invasive, doesn't matter if you took the shot from across the river or sitting next to your subject. You did capture a private moment. Its voyeuristic some may argue.
The question arises, where do you draw the line? When do you say, that could be a great shot but am not going to capture it. I do follow a few things. For lack of a better term, I am settling for etiquette. The basic principle that I follow is to avoid face shots as much as I can. That does take away a lot of the personal/intimate touch from the shots, but it allows me to focus on other things. Also, do remember that this is street photography and not photojournalism. There is a difference. And that difference means certain things are not acceptable to the SP community. The thing you'll hear everywhere is:
"If people don't want to be photographed, you do not photograph them."