Just a philosophical note for would-be streetshooters out there.
I've come to realize slowly that street photography is about INTERACTION - people (or animals) interacting with each other or with their environment.
This really came home to me yesterday while walking around at Stadium Cove. As I walked around, there were many beautiful subjects (human and animal) I could have taken pictures of, but I realized that taking them in isolation would be merely taking portraits, which is nice in itself, but does not have the added "zing" of a good street photograph (at least, to me).
What would add interest to the picture would be interaction. So I walked around with this one word repeating in my mind. INTERACTION. Look for situations where there is interaction going on. Or anticipate interaction, like the picture of the big dog and little dog. I followed the big dog around until it interacted with some little dogs, then started shooting. It was very easy yesterday, because when two or more dogs meet, they will surely interact (first thing they do is smell each others' backsides - wish people would do the same thing).