What a great topic....and I have commented on this below the PAD photo I put up today. I do a lot of "public" photos, but I am always thinking about the subject. In shooting our photos, it seems important to have some consideration for others.
When in public and we point the camera towards children, we need be especially cautious. Always, IMO, give your contact information to the adults who are in charge of children. I give an email address. Not doing this could create an embarrassing situation.
If shooting photos of a store front and the owner comes out and says not to, be cautious again. In some cities, the goods inside are not always "legitimately" obtained, and the store owner does not want this recorded. And in that case you may be dealing with a law breaking person who may decide to take things into his own hands.
Remember you may be "right" in the eyes of the law, but some folks may have other reasons for not having their photos taken. In fact, in some areas I have said out loud that if anyone has a hot warrant, indicate this as I definitely do not want to shoot their photo. This will clear out those who do not want their photo made, and they will usually not say anything, just get out of the line of fire. I say this usually in a joking manner, but everyone understands.
If there is an emergency, the photos must come second if you are a first responder and can potentially save a life. But, if an accident scene is ongoing and the professionals are working, this is a time to record life as it is taking place. Again, make certain not to get in the way. Talking to law officers while carrying your camera, inquiring about areas to avoid, etc., will lead to your being allowed to move more freely. Just walking by law officers can create a situation where they do not know who you are and then they become more controlling and may prohibit your actions or area of access.
And be very very careful when doing photo journalism shots as most often we are in unfamiliar territory and do not know what dangers may be lurking.
But the ultimate rule of thumb is to always avoid doing anything which is against another human being. Think before you shoot. I usually shoot before asking permission, but then chat with the subject after the shot. This gives nice spontaneity, yet allows your subject to be at ease about the photo you have taken. I will sometimes bring it up in the viewer and show them.
Well this is one of my experience....