We have several "bully" breeds in our neighborhood (two look like staffordshire terriers, two like big brindle boxers, and one I know is an English mastiff). I have never seen them do anything remotely aggressive towards me or my dog. Most of the time they seem to barely notice us walk by.
The dogs I'm most nervous about when we walk? A lab mix, a springer spaniel, an Irish setter, and a golden retriever (mix?). In all instances, I consider the owner are responsible for the behavior of their dogs. IMO, a dog who snarls and lunges at passers-by should not be left unattended in the front yard (when a perfectly useable back yard exists).
It is very unfortunate that this is true. To show that this doesn't always happen, I'll share my bad experience. As a child, I was bit by a German shepherd puppy (I could write an entire post on what went wrong in that situation). I'm still nervous around large, unattended dogs, but if I could provide the right home, I'd have a GSD in a heartbeat.
A woman in our neighborhood has a border collie and a chow that we often see on our walks. I'm always impressed at their amazingly good behavior - my goal is for my dog to be as well-behaved. Katie, my dog, stops in front the their house to look for the "pretty dogs."