My wife and I rode our bikes (the kind you pedal) from Vancouver, Canada to Monterey, California. The morning we rode in to SF through Marin county was one of the best of the whole trip.
We stopped in Monterey because riding started becoming less enjoyable. Through WA, OR and NorCAL, we would just leave our bikes leaned up against a supermarket while we would get groceries. Maybe not advised, but we never had a problem, and almost all the people we met were incredibly decent folks.
We met great people further south too, but the character of the place changed completely. Part of this is simply population density and the resulting issues. Whatever the reason, we just decided to rent a car and blast down the I-5. SoCal just seemed less inviting to cyclists.
Now I don't envy Northern Californians too much for the landscape, as I live in South Coastal British Columbia, which is every bit as beautiful. But I would happily get on my bike tomorrow morning and head south again.