I also was accepted to the Brown program and turned it down. From what I have gathered the competitivness of this program is highly dependent on your demographics (i.e. state residency (RI being greatly favored) and your ethnicity). I know a few kids from Rhode Island whose resumes were very good but not spectacular (sats maybe 1350-1400) who got into PLME. I know of one URM whose resume was unspectacular who got in (sats maybe 1200). I know of one out of state indian male with an extremely spectacular resume who was turned down (sats 1600).
I would say that these programs are competitive at the level of the average ivy school (excluding HYP).
As for me, I chose to attend a top ivy over Brown PLME. I couldn't be happier with my decision. It gave me a few more years to explore different fields so that I could be sure I was entering the field of medicine for the right reasons. I also am very glad to not be spending 8 years in Providence with the same small group of kids in the PLME program. I think these programs are a little odd. I had absolutely no experience in medicine whatsoever and I was accepted. Basically I just claimed I wanted to be a doctor and they said okay.
Finally, if you are really concerned with prestige (not that i'm arguing you should be), I will be attending a significantly higher ranked medical school next year.