The Slanted Door restaurant in the restored ferry building, fantastic - need reservations though - wont be disappointed. Also Asia de Cuba at the Clift hotel - on Geary - go for the food and carry on in the bar.
I lived there for a year and loved the City by the Bay.
24th Street is nice, laid back and a few cool shops and restaurants there.
Castro Street is great for a breakfast/brunch in The Patio Cafe - quality grub indeed.
The part of The Mission District down from there is very good, lovely Central American fare.
The Filmore mentioned, where the Mad Dog is, is fairly safe - most neighbourhoods are okay and get along fine with anyone wandering through.
SF is a chequerboard of ethnic or social variety - and they all co-exist in harmony.
Golden Gate Park is brilliant, nice for a stroll.
You can even go downtown in the evening and find decent bars and restaurants there - unlike most US Cities which are inhospitable after office hours
It's almost all good there - hard to go wrong in San Fran.