I found it WAY simpler to just bring a few thank you notes, write them at the end of the day, and leave them with the receptionist. That way I didn't have to remember to do them later, and it maximized the chance people got them before writing my eval and/or discussed me at the adcom meeting. Even though people say TY notes do not sway opinion, I know that I would personally have a more positive impression of an applicant had they given me a professional and thoughtful thank you card. And regardless, it is professional courtesy to send a thank you after any interview.