All the time, for all SF is a cosmopolitan place, its still very small, only 49 square miles, 25% of which is parkland. And the clubs are more or less in districts/areas clustered together, so the odds of running into people you know are high.
But everyone knows about me, so its no big deal, and here that sort of thing doesn't even stand out, what's wearing a dress at the Folsom Street Fair, it means you are the only person who is modest pretty much.