My wife and I will have a full week in San Francisco next spring. We will be staying in a centrally located condo (near Union Square) but will not have a car. What is the best way to get around downtown? Is there a weekly bus pass? I expect to walk a lot but I remember the hills too and can't imagine walking EVERYWHERE. I am also wondering with a full week if we would be wise renting a car for one day to go to Sausolito and points north.
Any suggestions?

Go to sfmuni.com for all of your transit answers (yes, they hae weekly passes). You can get to Sausalito by ferry (quite fun, too). Cabs are fairly easy to catch, too--you might pop into a hotel and have them hail one. BART is great for getting to/from the airport. If you get off BART at the Embarcadero, the Hyatt Regency is right there to catch a cab to the condo. Enjoy!

Yes, get a one week MUNI pass upon arrival. The streetcars and bussses are very convenient and easy to use (the cable cars are "just for fun", IMO due to the lines). GET THE OFFICAL STREET AND TRANSIT MAP. You can get it upon arrival ($3) or even better get one now to help plan your trip (On EBAY)

http://www.sfmta.com/cms/mrider/ridetips.htm#buymap

I think renting a car one day is a great idea. You might consider driving to Muir Woods first thing in the morning to avoid crowds, possibly Point Reyes if you plan to make a full day and hit Sausalito on your way back.

Another weblink for transportation in the bay area is www.511.org

No car needed to go to Sausalito. You can either take a bus (Golden Gate transit bus system) or better yet, take a ferry.

There is not much to do, the views are gorgeous, snap a couple of pictures, have lunch or dinner at Spinnaker, back to SF.

Now, if you want to continue north to the wine country or go to Muir Woods, it's a different story. Rent a car.