I used to live in SF and would love to move back there again. You will have a great time there. Make sure to bring warm clothes (layer works best) as the weather tends to be chilly in the morning and then warmer in the afternoon. Here are a few of my favorite things in San Francisco.

RESTAURANT/BAR
* The Slanted Door - used to be in the Mission, they just moved to the North Beach area (I think, I haven't been to the new location yet).
I just can't remember the name of some great restaurants there right now. But I know where they are.

* Tonga Room at the Fairmont Hotel - having a drink while listening to a live band and the "hourly" rain.

ACTIVITIES
* Ride the cable car (either Powell or California Street) - a fun experience.
* Napa is a must if you are a wine lover. It is beautiful in the valley and ... of course, there is free wine tasting.
* SFMOMA - beautiful new (a few years old) museum. Also checkout Metroen (Sony Entertainment Complex).
* Legion of Honor - gorgeous museum with breathtaking views
* If you rent a car (which I don't recommend), let me know. I have some other great drives that I can recommend.

Feel free to email me if you have specific questions. Have a great time in SF.

PS: there is no BART from the airport to downtown yet. Avoid Fisherman Whaft ... it is a tourist trap.