To answer your question why SF will likely weather the real estate storm: folks are highly educated, they have high paying jobs, SF is a unique culture not found anywhere else in the world, and the people who live in SF love it and don't want to live anywhere else. All that translates into folks that want to and can afford to stay.
Now about the misunderstanding with the Case-Shiller index and San Francisco. The index reports on the entire Bay Area. This includes places like Oakland, Fremont, Bentica, Walnut Creek, Vallejo and of course San Francisco.
These places have been hard hit by real estate slump. If you want to know about the general area, then it is a good index, however, comparing San Francisco with these places would be like comparing Manhattan to NJ. Really. Not only in proximity but also for the folks that live there. They are apples and oranges.
So, if you want to know about SF real estate, you're better off looking at a site that compares the performance of neighborhoods, year over year. Good luck!
Here's a site for condos:
http://www.sfcondosales.com/condocount - Tue May 13 2008, 09:09