Not a San Fran native but spent the summer of '87 in the Haight on Page St. and been there 10+ times over the years. If you're looking for some "couple" time - watching the sunset at Coit Tower is pretty cool. I love that city, my favorite US city to visit. I lived in Sunnyvale (just outside of San Jose) when my dad was in Vietnam in 68-69 and my grandmother was there till the early 80s.
Coit Tower view
A drive down to Monterey is worthwhile also - the 17 mile drive is pretty cool afternoon thing to do
This tree might look familiar - the Dead have used it for their video productions also on the 17 mile drive:
My wife is a literature geek - there's some John Steinbeck stuff in Monterey - Cannery Row etc. Also there's John's Grill on Ellis St was in the Maltese Falcon and had pretty good food from what I remember. We also drove up the coast to Bodega Bay the town in Alfred Hitchcock's "The Birds" very cool road up the coast.