Absolutely loved San Fran when I worked there a few years back - its probably one of the most "European" of the American cities. Night life is brilliant, loads of clubs around. Definitely do Fisherman's Wharf (the Clam Chowder is amazing, served in a cob loaf) and marvel at the farting seals. Take a taxi to Lombard street. Eat at the Stinking Rose (garlic with everything!). Take an excursion to Muir Woods to see the giant redwoods (remember the recent "Planet of The Apes" franchise films?) and take a shopping excursion to Sausalito. Cable car rides, chinatown, Alcatraz, Golden Gate, boat trip around the bay ... there is so much to do in San Fran!
Oh, and while you are in the area, hire a classic convertible and drive the PCH - it's one for the bucket list, the views are incredible!