As a native who's ridden here for over fifty years the hills are fairly easy to get around. Few will ride up Fillmore from the Marina for instance or California from the Financial District.
The new bike culture is centered in the flats. Valencia Street appears to be a major thoroughfare.
Most of my life I've lived on the Westside above West Portal and ridden around Twin Peaks instead of over them. I did find a route that takes you up Market St. (Clayton St) instead of going out to the Park and then up 7th Ave.
Best thng about the increase in riders is the sharing of routes. The wiggle is a perfect example. It follows a path of a water flow from an old lake, Sans Souci, on Divisidero to Valencia and Market. As such is has a very gentle rise to Oak and Fell. Obviously one could ride up Page st or Haight st but the elevation is much greater.
Being a bicyclist myself (I do obey traffic laws mind you) I can say that many folks like living near the "wiggle," the Panhandle and Golden Gate Park. More specifically, the Mission, Lower Haight, Haight, North of Panhandle, and parts of SoMa.