I didn't apply to the JMP program but a couple of the other applicants that interviewed the same day that I did, were also interviewing for the JMP program. One of the applicants who had been to the Berkeley interview for the JMP program said that there were barely any lectures in the program and it was pretty much all group discussion, although, you might want to comfirm this. Citygal, I think it is, who started another UCSF link is a very helpful UCSF medstudent who you could ask.
The thing that I learned about UCSF, is that there is a lot of opportunity to pursue these programs as UCSF med students. If you are not sure that you want to do the program now, but you think you might decide to later, you might not want to apply for JMP 'cuz you will have the opportunity if you decide to do it later. On the other hand, it won't hurt your chances of getting into the MD program if you apply to the JMP program, so why not? Also, do you want to be in Berkeley or SF for the basic science years? UCSF is a health sciences university while UC Berkeley is a GIANT university with many other disciplines. They are very close (30 min depending on traffic), but definately different cities.
Well, just giving you some things to think about, I am not sure how much I helped. But that's awesome that you received a secondary and I definately think you should continue to apply and maybe (please, oh please let me get in) we'll be classmates next year. I can't emphasize enough what an awesome school UCSF is. BIG sense of community (med students not involved in the admissions process were just coming up and talking to us all day during the interview), awesome faculty, and in San Francisco (awesome views).