Penn also has a 1.5 year basic science cirriculum, allowing you two rotations before beginning grad school.
As for merits? I think the two big ones have been named. Demerits? I can't think of any. I think that conventially most schools go for two years of basic science and then break for grad school, and it's just hard to break conention. There seems to be a lot of resistance to shortening cirriculums, but it's happening more and more. I wouldn't be suprised if some programs let you do a couple rotations even after doing two years of basic science and going into grad school, but this would be up to the med school.
Duke has a 1 year basic science cirriculum. The MD/PhDs there typically do a full year of clinics before leaving for graduate school. Adding Duke to all the other schools listed in the thread completes my personal knowledge of clinical clerkships pre-PhD.