I did (am doing) the SMP at georgetown. Although I'm probably biased, the "word" is that it is the best masters level post bacc program (and thus the only one I applied to). Of all the schools that offer these MS programs, GU is arguably among the best.
I know many of my classmates that got multiple acceptances that didnt get any interviews at all last year and the only thing that changed in their app was that they were a year older and enrolled in the program.
I thikn that if you are already a good applicant these programs wont help you much. If say you hvae excellent MCATs, or your gpa is above a 3.4 or so, these programs are more like "insurance policies". It really depends on your individual app. I think these programs are great for people with decent MCATs but a low GPA. They'r emeant to prove you can handle the coursework. If you hvea a good GPA< these programs arent nearly as helpful as raising your MCAT.
They also do a good job of preparing for your MS1 year. PM me your stats if you want and I'll give you my opinion on you going ot one of these programs.