Like Jude, I'm a newspaper photographer and in the eight years I've been doing this, I've never asked someone to sign a release. In most cases, we do ask for names (and sometimes where they live and their ages, if they're children.) When photographing children, I always ask permission to use the shot. I often take shots prior to asking, but then introduce myself to the mother or father, tell them I've just taken a picture of their child and ask if it's all right to use it in the paper. Even in a small town, there can be issues where it would not be a good idea to have the child's photo published.
I've only been told not to use a shot twice - both times related to children. Using a digital camera, I showed both people that I was deleting the shot.
As far as being told I wasn't allowed to take a photo of something, I've rarely been told that and I usually - politely - reply, "Well, yes, I am, but .. if you could please tell me why you would prefer I didn't, I'd be happy to consider that." The time I was taking shots of a drug raid and undercover police were involved, I acquiesed because having their faces in print could have endangered them. What I didn't do, however, was let them take my camera or my film. And yes, they asked for it.
Some of my photos are taken while technically 'on the job', but my editor knows and doesn't mind, even if some of them are the same or similar to things she'll be running. She is actually rather proud of the fact that I like what I do for them enough to use the photos here to share with all of you.
I do thank Aestus for posting the links to the attorney sites on photography in public places .. very, very helpful stuff to know.