It sounds like you're treating an Apple building downtown differently than any other skyscraper. It's still just a big tower filled with people. Are you saying that SF is literally bursting at the seams and that it can't support another big office tower? What about the giant Transbay development plan? If you're going to stuff 12,000+ people anywhere, it's better to do it in an already dense area to take advantage of efficiencies.

Green Metropolis is an interesting read about big cities and sustainability: http://www.amazon.com/Green-Metropolis-Smaller-Driving-Susta...