I don't own a car, and don't know that many friends that own a car. You get around with BART, MUNI, Lyft, Uber, taxis, biking & walking.
Usually I only need a car when visiting South Bay, and then I take Zipcar.
I've had a car the entire time I've lived in SF (8 years), and it's been great (makes it possible to be spontaneous). However, I've always lived in neighborhoods where parking wasn't a problem.