After hours, the city’s business folk and workers give way to costume-clad partygoers, hippies and hipsters, downtown divas, frat boys, and those who prefer something a little more clothing-optional. Downtown and the Financial District remain pretty serious even after dark, and Nob Hill is staid, though you can't beat views from penthouse lounges, the most famous being the Top of the Mark (Hopkins). Nearby North Beach is an even better starting point for an evening out.
Always lively, North Beach's options include family-friendly dining spots, historic bars from the city's bohemian past (among them Jack Kerouac's old haunts), and even comedy clubs where stars such as Robin Williams and Jay Leno cut their teeth. In SoMa there are plenty of places to catch a drink before a Giants game and brewpubs to celebrate in afterward. SoMa also hosts some of the hottest dance clubs, along with some saucy gay bars. While Union Square can be a bit trendy, even the swanky establishments have loosened things up in recent years.
Heading west to Hayes Valley, a more sophisticated crowd dabbles in the burgeoning "culinary cocktail movement." Up-and-coming singles gravitate north of here to Cow Hollow and the Marina. Polk Street was the gay mecca before the Castro and still hosts some wild bars, but things get downright outlandish in the Castro district. Indie hipsters of all persuasions populate the Mission and Haight districts by night. Keep in mind, though, that some of the best times San Francisco has to offer are off the beaten path. And a good party can still be found in even the sleepiest of neighborhoods, such as Bernal Heights and Dogpatch.