Depends on the residency. Do you know if its a group of people that select/interview you, or is it just that PD? I'm doing anesthesia and I know at my institution my PD rarely talks with the other attendings, and those attendings are more or less in charge of the selection/interview. It would be nice for them to know what the PD thought just in case he didn't go out of his way to describe you. You have to remember, your selection is going to be a group process, even the educational coordinator and secretary have some sway.