I live in NorCal so I'll defend my part of the state. In Marin county, the drivers are pretty considerate. In a year and a half of road riding, around 3000 miles, I've only had one bad encounter. A large truck passed very aggressively on a rural road when there wasn't any traffic around. I didn't think that much about it. I think I said, "whoa" to myself and left it at that.
I would have to say that some riders are more prone to negative encounters. Be it personality or riding style.