I'm thinking of sending a thank you letter to the program director at a site where I interviewed, but not with the PD himself (this was an internship program). It just doesn't seem appropriate for me to send thank you notes to individual interviewers with whom I only spent a half-hour (and who are probably not part of the selection committee anyway).
You can do what you think is strategical, however last year I sent individual thank you letters to each and every person who interviewed me. I just wrote them while I was waiting in airports or sitting on the plane.
It may seem like they "only" spent a half hour with you, but multiply that times the 5-6 candidates for the day and consider the time they took from their schedule and I would say you should be a little more appreciative, regardless if they are on the selections committee or not.
Remember, even if you match at that program successfully...you may be working with each and every one of those attendings who interviewed you and it behooves you to not be the one who didn't thank them for their time.
