Hi Pat--It's my opinion that the San Francisco neighborhoods that are hot become that way because they offer a particular type of housing stock that corresponds to popular price points and to popular commuting locations.
Over the past year, properties under $1M have been selling briskly. The types of properties I've seen go quickly into contract are two-bedroom condos in very walkable locations (Mission, Hayes Valley, South Beach, Noe Valley, Mission Dolores, Haight, etc). We have a lot of technology workers in San Francisco who commute to the Peninsula and downtown, and these areas facilitate commutes. Also selling well are single-family homes in the Excelsior, Bernal Heights and Miraloma Park.
Neighborhoods in the north end of the city will always be "hot" in the sense that they are the gold standard in real estate. Development is sparse and you're pretty much working with existing housing stock. Property values tend to hold up well over time.