If was going to San Fran for a wedding i would stay in Napa and drive in for the wedding. We stayed here last time:
http://www.villagio.com/villagio/home.html
Last time in San Fran we stayed at the Sheraton on Fishermans Wharf and the hotel itself was ok...the villagio was so much more enjoyable.
Watch out for "bushman" at Fishermans Wharf while you are there. He is certainly entertaining:
Also, Beach Blanket Babylon is an incredibly amusing broadway style show that in my opinion is a must see.