This mate, have a meal in ChinaTown its far better then New York. Fishermans warf is ace for Chilling.
Theres some cool places to hang out in the Castro (used to be a gay hotspot, but far more mainstram these days), Haight/Ashbury worth a look.
You could get the bart out to Berkley as well.
There is an ace hike up a small mountain just out side the city - cant remeber the name now.
Rent bikes and ride out from fishermans warf - to the Goldan Gate and go cross.
Alcatraz.
If your there for a while, you could shoot out to Vegas for a couple of Days. Trips are run to and from in the City. Weekend is enough.
If your looking for a cheap hostel, try the green toiroise - free keg parties, beer pong, free internet, guys that run it were about in the 60s and are shall we say tolerant. Walking distance from the City & Fishermans Warf, couple of streets from China town.