Some people make a big deal out of the MED program here. But to be honest, I think how you do here as a dental student is much more of a reflection of your work-ethic (and to some degree inherent smarts), and not so much just a mirror of what you do to prepare. MED is ok in that it "eases" you into the first semester a little bit (only for about two weeks, whereas some poeple's undergrad got them through the whole first year), but... if you find yourself struggling with MED, dental school will destroy you as MED is still a watered down curriculum as far as volume goes. Althought I guess that could be a good indicator as well... In true comparison to dental school it's a lot like 3 or 4 high school band members up next to a 120 piece orchestra as far as overall effect. Notes may be the same, but intensity and volume is totally different.
I will say that the UNC admissions committee is aware of MED participants. But it most of the time it only minimally enhances an applicant in the eyes of the committee; rarely does it serve to "make" an applicant (unless they get a like a 4.0). Hope that helps.