When we have our rank meeting (includes PD, other attendings, and current residents/fellows), it's not unheard of for someone to mention an applicant's FB page. More commonly it's residents, but I've also seen our PD and a couple other attendings do this as well. Usually it only gets brought up if there's something kind of questionable, and the context is whether the applicant is demonstrating "poor judgment" by posting it.
In other words, for most applicants it never gets mentioned, but in a few cases it clearly works against people. Never seen anyone in our rank meeting mention anything on FB that made a candidate seem like a better or stronger applicant.
The privacy settings are important, but not the whole answer. In some cases the applicant had FB friended one or more of the residents during the interview season, or maybe while doing a sub-I here, so the undesirable information wasn't really that well-protected. I guess just assume that anything you put on FB has the potential to be looked at by a PD, so post accordingly.