I just had a job interview for a tenure-track position where I interviewed with several people from the department. As far as I know, I'm supposed to send a thank you note after the interview. Should I send one to each person I've interviewed with or would this be perceived as excessive?
If you feel that you want to thank members of the panel for their time and consideration, go on and send them a brief note. In my experience, it is usually impossible to exclude one or two people from the list without irritating someone, so I would say — write to all of them or none. It is natural to feel that a communication like this is "meaningless", "time-stealing" and "unnecessary" — long story short, it is not. A senior academic receives a ton of spam and unrelated correspondence, which they delete with a grunt. Make your message short and positive, and they will delete it with a smile.
If you are planning on sending the notes because you think that it will improve your chances of being hired, don't waste your time. If two candidates were equally good in terms of their CVs, and equally collegial during the interviews, which they never are, then maybe, and only maybe, would the thank you not matter. As soon as one candidate is even a hair better than another, then the thank you note is not going to matter.
If you want to send thank you notes because you appreciate the time they took out of their schedule and you enjoyed talking about their research, and would like to potentially collaborate with them, ask them for feedback in the future, etc, then send them a thank you note. Job interviews, even if you do not get the job, are a great opportunity to network. A thank you note is a way to continue the conversations that were started during the interview. They are not an effective way of increasing your chances of being hired.
I think the only way it would be excessive would be if you thanked people whom you had no reason to thank.
Considering the phrase "thank you for ___": If you can fill in the blank with something reasonable like "inviting me for an interview" (to the person who actually sent the invitation,) "taking the time to meet with me," or "showing me around the campus," then it would be nice to send a brief note to the person saying as much. These days I think e-mail would be perfectly appropriate.
On the other hand, if all you have to thank someone for is considering your application, then there would probably not be much of a point in sending a thank-you note to that person.
A thank-you note can be useful if you're trying to gauge the department's excitement about your interview. An effusive and excited response might indicate a sincere interest in the candidate, whereas a terse, closely-guarded response could indicate a tighter competition for the position (or a lack of interest ... or an antisocial professor ... or a bad hair day).
I'd chasten against reading too much into the response - it's easier to ask directly from someone in the department with whom you have made some contact. In fact, this is much better than a "thank you" note, as it does not suggest an unduly attempt to influence a decision.