There are certainly valid points in both sides of this argument: Drizzt, I agree scripps, BM, and Goucher are def. in the top 3, but I would argue that Harvard is the #4/5 post bacc in the country, a fair assertion to be sure. Although, I do recognize that a notable step exists between the #3 and 4 schools.
I attend HES and I must say that the program is very strong. It has tremendous regional advantages for those of us looking to attend Yale/HMS/Dartmouth/Columbia because of the connections between the adcoms and the program directors. The directors, Dr. Fixsen and Owen Peterson are tremendous and will goto great strides to aid in the process. Further, and this is simply my personal experience, all my professors have been Harvard Instructors, two of which teach at HMS. I have developed close relationships with these instructors, relationships that will surely aid in my application's competitiveness.
Furthermore, there exists an intangible advantage of being at HES that is a little bit outside the realm of relevance. There is an intrinsic honor and confidence that one feels from being part of the Harvard tradition, a confidence that is necessary in medicine. There are times when I will goto the Harvard football game with my gear on or study in Harvard Yard, and these activities help me to release stress and do well in the program. Furthermore, the Diploma in Premedical Studies students are truly Harvard students. They have Harvard IDs and all the privileges that come with the IDs. Further, they can join the Harvard Alumni Association and local Harvard clubs to network for clinical internships.
HES is certainly not as strong as BM, scripps, or Goucher but it is a great program with superb educational quality and regional connections.
I hope this helps to clear up some of the haziness about the program.