A word of caution - if you are used to the NYC system you may be a bit disappointed with the SF system.

The trick is to figure out where BART (Bay area rapid transit - connects city's in the bay area) and MUNI (sf system) stop in SF. If you find a job in the south bay find a place near the cal-train station so you can easily walk or bike to that since it is really the only option for getting to silicon valley besides company sponsored buses (most of the big tech companies run these from SF)

You want to avoid the MUNI buses except the ones that are a straight shot to downtown. Find a neighborhood with a MUNI subway stop or BART subway stop. I drive to the south bay and my girlfriends commute in sf (Two busses) takes the same amount of time, about an hour, to go from the inner richmond to fisherman's wharf. This is about your worst case scenario for public transportation in SF. If you choose your neighborhood wisely you will be fine and the zip cars are everywhere as starkfist already mentioned.

edit: Guide to the neighborhoods - http://www.sfgate.com/neighborhoods/sf/

You should definitely live in San Francisco. You'll miss out on some things, but you can live well there without a car.