I have a lot of experience with dogs as a volunteer at a county animal shelter and I have a healthy respect for any/all breeds and mutts. Any breed or dog can be dangerous. Find out about the dog before approaching. Remember, a wagging tail isn't always a sign of friendliness. And, with the exception of those breeds with a "natural" smile (Goldens, Labs, etc), a smile may be a warning of bad things to come.
That said, I am more careful around Rotts, Dobermans, and Chows and won't go near pit bulls.
Muriel