I wasn't that impressed with UCSF's residency. I think Stanford's was more competitive last year, IMHO. I ended up ranking UCSF lower than the residency where I ended up (UCSD).
I'm not really sure that they only take MD/PhD's, but the relatively new UCSF chair, Abul Abbas, is a scientist rather than a clinical (ie practicing) pathologist, and indicated to me that he encourages his residents (particularly the MD/PhDs) to do basic science as much as possible. He told me he was disapointed to hear that I wasn't dedicated to a career in the basic sciences. My response is--why bother doing a residency when I could go straight to a Post-doc? I'm doing a residency primarily to become a good practicing pathologist. Research is just icing on the cake. (I'm an MD/PhD, BTW).
It probably wouldn't affect the residents, but there are rumors that the faculty is unhappy with Abbas and what he is trying to do with the program. I know my program has benefited directly by getting two top notch faculty that defected from UCSF to UCSD shortly after Abbas took over. However, there are alot of faculty that are fine with Abbas, and strife amongst the faculty is unlikely to affect the residents anyway.
To be fair, there are some great things about UCSF--it's a great, world renowned hospital with fantastic specimen volume and variety. Abbas has set up budgets that residents can access freely for research purposes (with little to no oversight). I really liked the residency PD (tresseler), and got the impression that he is popular with the residents. The city itself is a mixed bag--lots of stuff to do and see and very beautiful, but very, very expensive. The salary at UCSF is a little higher than other residencies, but the cost of living is much higher.
anyway, good luck with match. remember that all of the above is just my opinion, so take it with a grain of salt.
-mrp