Its kind of a coincidence that today I was talking to a friend of mine who's a MS1 @ UCD, he told me all about this med site and I was checking it out when I came across this thread.
I'm in the Class of 2006 at UCI, and from my first had experience I'd say the quality of instruction is comprable to UCD. Both have small class sizes for UCs. My friend at UCD tells me that patient contact began the first week, I didn't see a "real" patient until I signed up for a tag-along with an Oncologist in November. The curriculum is the biggest difference in my opinion, Irvine's is of an integrated, organ systems nature where Davis is a bit more conventional. Small group learning is utilized at Davis from the start, here we'll have our own problem-based learning groups formed in the second year, but many students participate in the Medical Scholars program during the first year. Both schools have medical centers that aren't on campus, so having a car is a given.
I don't really know if it costs more to live at Davis since I live with my S.O. and her sister. I'm a bit biased towards Irvine b/c I was rejected pre-interview from Davis, but my friend who's there was accepted to Davis first and then pulled off the wailist here, but didn't think twice about it. He's from SoCal and his girlfriend is an undergrad at UCI, but he felt Davis was better for him b/c it was more widely recognized.
I didn't have the same choice, but I don't mind this school at all. The professors are great, the exams are board-style, and the schedule isn't as demanding as other schools, like UCSD. It might only be my class, but I was surprised that my fellow students aren't really diverse. First day of orientation I got into a heated discussion with a fellow student about the causes of poverty, and from my experiences, you might have to grow a thick skin if you're not rather conservative.
I can't tell you if I would have picked one school over another b/c I wasn't in the situation, all I can say is that I don't regret coming here.
P.S. If you do come here I recommend doing the summer pre-entry program, you can get on-campus housing that way and the review really helps for the upcoming year.