I can't say it would really make a big difference to get a "thank you" and I've never sent more than cursory thanks.
One thing I have done, though, when interviewing for a job, is to not ask all my ?'s when the interview enters the "what do you have to ask about us?" phase. I try to keep one in reserve and send that to someone in my interview loop after the fact. I feel that it shows continued interest in the position and I have never gotten a negative reaction from anyone for asking a follow-up ?.
One thing I have done, though, when interviewing for a job, is to not ask all my ?'s when the interview enters the "what do you have to ask about us?" phase. I try to keep one in reserve and send that to someone in my interview loop after the fact. I feel that it shows continued interest in the position and I have never gotten a negative reaction from anyone for asking a follow-up ?.