I got into the San Marcos campus... looks like there are only 2 of us on here so far.
I think that the reason that most people seem to prefer the San Marcos campus is because it is alot closer to a) the coast and b) the greater San Diego area. For those of us that already live in "San Diego", going to Temecula would be quite a commute. It would be at least an hour for me. I honestly don't know all that much about Temecula because I've only been there a handful of times, mostly to visit the wineries and go wine tasting. From what I have seen there isn't a whole lot to speak of, but the nice thing will be that rent will be cheaper! I remember it being very pretty and scenic, but def not a bustling metropolitan area.