When I lived in SF I would ride pretty everywhere. The SF Bike Coalition is one of the most effective lobbying organizations I've ever seen, and they've done a huge amount to transform the city to make it bike friendly. In return, the number of people biking has really skyrocketed in the last 10 years. There are often good bike lanes along routes, and sometimes they are even separated. They have a pretty good map that shows you bike lanes, so you could use that to plan out some routes while you're getting familiar.

Anecdotally, the motorists are more aware of bikes now than they used to be (just because there are more of them), but you still need to ride pretty defensively.