I've never lived on the east coast so I can't say from personal experiance but from what I gather from people who have lived on both coasts, Californian's are more laid back, nicer, and less pretentious than New Yorker's/East Coast people. I hear that the East Coast is more old money, class based, and snobby, the west coast is generally not like that. Some really wealthy areas can have snobby people here, but I think that's the case anywhere you go.
Some people from the east cost talk about how they prefer that "in your face" type of NY attitude b/c they think it makes them more "real" or something; people aren't like that here really.
I think people in CA are generally nice and really laid back, SD I think has some of the friendliest people in the state. I think it's maybe b/c the great weather puts people in good moods a little and most people here are transplants so we're all kind of down to meet new people. Most people from NY/NJ area here in SD, which there are a lot of, are pretty nice and friendly too, maybe CA just attracts the more laid back type NY people or they just chill out when they get here.
I think Californian's are nice, friendly, and laid back overall and we are not like all those stupid stereotypes you see in the media from shows like Laguna Beach, 90210, The OC or whatever lame tv show based on some glorfied and untrue image of CA life. Most of us are normal, hard working americans just looking to live our lives and enjoy the sunny CA lifesyle.