I think a few schools have had orientation starting July 31 - and I think some Eastern schools don't start until September. I think my experience this year was pretty typical for a state school - orientation started Wednesday, August 10, and classes started the following Monday, August 15. I don't know about other medical schools, but we have 18-week semesters while the rest of the University has 16-week semesters.
The University of Oklahoma College of Medicine - Class of 2010