I'm not surprised that residential real estate prices and rental rates keep climbing in San Francisco when there is a slump in much of the rest of the country. There are several anomalies at work here, but none explain the phenomenon.
I wish I could pin it on the City payroll which is
gigantic. The City payroll last year was over $2 billion, employing
over 27,000 workers. That is $75,000 per worker (including taxes and
benefits). There are almost 3,000 workers and politicians earning over
$100,000 on the payroll. For every City worker who lives outside of San
Francisco there is Federal or State worker who lives in San Francisco,
so the number, 27,000 is a good indicator of the impact of the City
payroll on the City.
San Francisco has the highest number of city employees per capita of any American city.
The City has a high gay population by all
data estimates. I estimate the gay and lesbian population at 100,000,
Gary Binder a local survey researcher puts it at 80,000. That offers a
large number of well educated workers who can combine both their
incomes for rent or home purchases. (The 2000 Census, found
self-described gay couples to number a little over 10,000 for San
Francisco.)
The
City also has rent control. There are 650,000 people living in San
Francisco, they form 340,000 households. Of these, 130,000 (40%) live
by themselves, 200,000 (30% of the units) live with one other person
(100,000 units), the remaining, 100,000 householders live 3 or more
together (in the remaining 80,000 units). 
There are 310,000 housing units in San Francisco. Two thirds of all units are rented. Three-quarters (75%) are rent controlled. That leaves 155,000 residential housing units that are not rent controlled; 110,000 of these are houses. The 155,000 are exactly half of all residential units.
Less than 20,000 rental units come on the market each year. About 5,000 homes come on the market.
The City also has a very large population of high paid biotech researchers and an even higher population of trust funders who can afford to live here. I can't figure the number in the trust funder category.