Headed to San Fran for work this fall and staying an extra week, what falls into the 'must do/see' category?
As horraybeer said, Yosemite Valley is a must see if you haven't been there before. I would recommend seeing it during the week to stay out of the traffic jams that happen there on the weekends. Depending on how much you want to cram in, you could drive over Tioga Pass in Yosemite and see Mono Lake and Lake Tahoe on your way back to San Fran. Of course depending on how late in the fall you are talking about, snow will become a factor to consider.