Hang in there everyone! Having (unsuccessfully) weathered UNC's admissions process last year, I can tell you that the temporal pattern of acceptances can be quite arbitrary. You could have interviewed in September and not hear about an acceptance until spring. UNC is one of the slower schools, and (for better or for worse), not hearing back soon after your interview isn't necessarily a "hold." Definitely don't count yourselves out this early in the process!
Also, FWIW, Joni told our interview group that we should not send letters of interest unless we have something truly substantive to add to our files.
I too am eagerly awaiting a response after interviewing in early October! My ADCOM was Dr. Houpt...anyone else have him?