San Francisco is a center of sexual experimentation. The
NYTimes published a piece by a local S.F. writer; she discovered a group of women who have formed a commune with a few men all of whom focus on the female orgasm. Glad to hear about it; but I'm not the least bit surprised.
The group grows out of a 1970s communal sex group, I knew well, called Morehouse in the East Bay, that still exists.

Why should this be a unique phenomenon of San Francisco?
Catherine Campbell is due credit for the explanation of this one. Catherine, a brilliant analyst of San Francisco life, used to say: 'San Francisco is a crucible, people come here to find out who they are.' (Then they usually move to where they will most likely succeed.)
Sexuality is indeed one of the most prominent elements of the San Francisco crucible. San Francisco is certainly the center of sexual experimentation on the American continent.
Jefferson Poland started the Sexual Freedom League here. The world of Sadomasochism has long been focused here, we call it leather. The leather porn video capitol is here.

The first PhDs in human sexuality started here at the Institute for the Advanced Study of Human Sexuality an outgrowth of the National Sex and Drug forum (founder Ted McIlvenna, my friend). PhDs are still given here. My co-author Salli Rasberry started the first sex film festival here.
The public gay (after WWII) and lesbian movements started in SF, (founders Phylis Lyon and Del Martin, my friends), as did transgender surgery at local Stanford and the VA hospitals. Good Vibrations, the first retail vibrator store, started here (more friends).
There really is no end to the list. San Francisco is the sex capital of the American continent, has been and probably will continue to be.