My understanding is that "preference" is not given in the same way that it was for undergrad or medical school. They don't have a quota to fill for % of students coming from CA because they're not principally supported with CA tax dollars anymore - at this stage, it's federal money footing the bill. However, I think when considering whether or not to grant you an interview PD's will consider how serious you really are about their program - e.g. if you grew up on the East Coast, and stayed there for college & med school, you might have more work to do to prove that you really are serious about moving cross-country for residency. However, I am sure they are familiar with Californians who had to leave for medical school and want to return for residency, and don't think that they would hold that against you.
I myself am from CA, and though I chose to leave for medical school, I now desperately want to go back (I'll be applying this coming fall). On that note, here's a question - do PD's have access to a list of the programs you've applied to? I am assuming the answer is "no", but in my case i wish they did. I plan to apply to every single program in CA and bordering states + my home program (and nowhere else in the NE/South/Midwest), which I figure would make it clear how serious I am about returning to the west coast.
