Only been out here about 2 years after New England hiking and backpacking, but I'll second what others have said above - excellent hiking within easy reach including state parks such as Big Basin big www.basin.org (largest redwoods concentration south of Redwood National Park, has 7 waterfalls, winter is a great time to visit), Midpeninsula Regional Open Space District parks http://www.openspace.org/ , etc.
Some backpacking nearby such as Pt Reyes, Henry Coe, Mt. Diablo, etc.
For backpacking with grand scenery, several hours drive to the Sierras - Yosemite, Kings Canyon, Tahoe, etc. Trinity Alps very nice too from photos I've seen. Fall/winter is a beautiful time to visit the Sierras.
Great local hiking resource with detailed trail descriptions: www.bahiker.com
You can get very good backpacking trip ideas by checking out the SF Sierra Club and UCSF/Stanford/UC Santa Cruz/UC Berkeley outdoor programs upcoming and past backpacking trips as they run so many trips. Also trip reports here on BPL.