There's always been a split in how Californian's view themselves. The N/S thing has been going on since at least the late 50's. One of the big factors is that there is almost nothing for almost 300 miles between the Bay Area and Los Angeles. (with the notable exception of a large part of California's Central Valley... which while representing only 1% of farmland in the U.S. produces 8% of our agricultural output). Another factor is that Southern California is way more conservative than Northern California, even with the "Hollywood" influence.
As for native Californian's you'd be surprised. There are 38 million people there and my guess is at least 2/3 of them are from there. I used to live there and still go there for work/pleasure 8-10 times a year and I encounter as many people from there as any place I've ever been. The thing is, in my experience native Californian's rarely move to other states. I don't know the hard statistics but I bet California is in the top 5 states in retaining residency of people that are born there.