Historically it has been a positive, as it's allowed for a more cooperative learning environment. This is especially key as the 1st year in UCSF is the hardest year (depends on the school whether they frontload the material or dump it on you the 2nd year), and sharing of study materials helped me pass.
With NBDE Part 1 switching over to P/F as well though, it gets rid of the only differentiator that existed for UCSF students. However I've heard rumors that they'll be coming up with other specialty exams to supplement this?