(1) Don't get so caught up in sightseeing that you don't take any time to just walk around and enjoy the city. SF is a vibrant place, with an incredible urban feel going on - I actually like it more than New York in that reaspect. But you'll never get all this if you are running from sight to sight trying to check things off a list.
(2) Go to Chinatown - very interesting. Oh, and get off the main tourist street that sells knicknacks and go one street over to the real chinatown. The Frommer's guide to San Francisco actually has an excellent suugested walking tour of Chinatown in it - I recommend it.
(3) If you have a few extra days, go south on Hwy 1 and spend some time in Big Sur. Gorgeous area.
(4) A good day trip out of the city is Point Reyes national seashore. Also gorgeous, and you'll go by Muir Woods on the way.
(5) SF has some wonderful restaurants.
(6) Unless you are there a long time, don't obsess about your workouts and such. There's too much to see and do to spend 2 hours every other day in a gym (in my opinion) and a week off isn't going to hurt you. And you'll likely be walking enough any diet transgressions will be minimized (don't go hog wild obviously :D)
(7) HAVE FUN!