Was over last June, no bikes although I was as happy as a pig in **** with a Mustang!
SanFrancisco and its surrounds has a massive biker presence. Bikes on evry residential street (mostly SV's from what I saw) Some amazing roads south of the city. One of the most famous spots is Alice's Resteraunt at the crossroads of Skyline Blvd.35 and La Honda 84. Big biker haunt at the weekends and cracking scratching roads abound in them thar mountains.
If you can wangle the time head for the Big Sur coast. Monterey - Morro Bay. Quite a way south but I would imagine do-able over a weekend. (We drove leisurely from SantaCruz - Santa Monica easily in daylight, as a measure). Mind blowing road, twists and turns, up and down. Have rode similar in Europe but this is a beast and goes on for ever. Jaw dropping views too.
Yosemite National Park is another must if you have time. Not that great to get to from the west (stereotypical flat straight american roads) but some top roads heading north out of the park towards Sonora and all the old gold mine towns.
In the city check out
http://www.acecafesf.com/ . Ex-Brummie owner. Loads of race memrobilia on the walls, good beer and food. Show the racing if its on. Some cracking characters. Don't chip the ball off the pool table unless you want a heartattack.
Like anywhere else, where the hills and mountains are, are the best roads. And they have plenty. Enjoy.