The California Academy of Sciences' weekly Nitelife event has been a smash hit since its launch in February. It's hard to beat the $10 cover (as opposed to $25) and the adults-only setting, sans the baby strollers and teenie-boppers.
We went a few weeks ago, and the place was packed. We kept hearing everyone exclaiming to their friends how it was like a nightclub, and we met an Australian who was amazed that San Franciscans are so into science. (We do hear that the spectacular new building is what sparked everyone's new-found interest.)