It was only last year that the Bank of America Center, long the dominant building in San Francisco's financial district, was sold to a group of New York investors for an impressive $825 million. Now the 52-story reddish-brown granite tower is said to be going on the market again. This time, the sellers are hoping that the price will reach as high as $1.25 billion. In recent weeks, the feverish residential market has spurred incessant talk about the prospect of a housing bubble. But prices for commercial real estate have also been going through the roof, despite high office-vacancy rates...