It's not that San Francisco is inherently different from other cities. It has the same bustling pace and seedy nature that plagues (or blesses) all of them.
The separator lies in the attitude of its residents. People here are either expressing themselves fully or at least encouraging others to do so. Whether they're selling "genuine American art" while sitting on a trash can or playing a street-corner guitar slightly out of tune, they do not fear harassment or even ridicule.
"We have patience," the city seems to say. "You keep practicing until you get it right, or at least to your satisfaction."
Folks here realize that even such attempts are better than stifling frustration, a void of expression. Everyone has something to offer.