SF Chronicle explains:
Prop. F sought to limit vacation rentals to 75 days a year; beef up enforcement and penalties; and establish big payoffs for neighbors and others who successfully sued violators. The measure’s backers, a coalition of housing activists, landlords, neighborhood groups and hotel workers’ unions, said the city’s existing regulations for short-term rentals, enacted in February, are toothless. They noted that only about 700 of Airbnb’s thousands of hosts complied with a requirement to register their homes as temporary rentals.This is a pretty impressive victory in the People's Republic of San Francisco, where lefties have generally been successful in stopping change, progress and innovation. It's the new techies who are changing the voter demographic.
To be sure, this isn't a complete libertarian victory. It does seem to limit options on the way landlords can draw up their leases, but it is certainly much better than the draconian restrictions called for in Proposition F.