First off, I think it's WRONG to leave your dog in a public place without someone you know watching it. Any moron could come up, feed your dog something, take the dog, or do something to the dog without you knowing!.
I agree with you KayAnn, I would, and never had left my dogs out somewhere. I remember a friend wanted me to once with Rufus, but I was so paranoid someone would take him or do something to him.

As for going up and patting one, I don't know if I would, I don't think I would..