I just finished my first quarter at UCSD and I didn't think it was bad at all (first quarter is just P/F w/o honors). My classmates are awesome (although this doesn't really distinguish SD since most med students are a pretty remarkable bunch in general) and everyone in class has a great sense of humor. I haven't met any gunners (if you define gunner to be someone who goes out of their way to excel at the expense of others). We do work very hard here, but I think every medical school necessitates a considerable amount of work. There was a controversy last month about grading policies not being sufficiently clear, but the administration moved very quickly to address our concerns. The weather is unbeatable and coming back to the Bay Area for Christmas break has been a little depressing. Once you get used to all that sunshine, three straight days of rain can get you down.
But to address your initial question:
Pros: Weather (if you're a fan of doing anything outdoorsy, this is the place to do it), classmates, frequent free food
Cons: Longer class hours (although some are somewhat optional). Now our official "class hours" eg hardcore basic science lectures aren't any longer than other schools, but we have a bit more fluff classes than other schools. By fluff I mean classes that aren't really essential but contribute to your road to doctoring in one way or another: journal reading group, small group ethics discussions, etc. I don't think fluff classes are useless, but they do eat up quite a bit of time.
I am very happy with my choice. It's close enough to home that I can visit every other month, but far enough that I am shielded from family drama. I am a Cali resident and despite the tuition hikes, after the financial aid, this place was still a steal. I think the best thing for you to do is to come here and take a look for yourself. You wouldn't buy a car without test-driving it once or twice...why would you choose a school solely based on the opinions of others? Ultimately, it's about finding a good fit for you.