I am in the process of interviewing for faculty positions and trying to keep my CV up to date as I go. Should I include research (or teaching) presentations given during on-campus interviews as invited talks? Or are they considered just a part of the interview process and better left off the CV?
I disagree with Dave. An invited talk is, by definition, a talk that you've been invited to give. Yes, interviews count. (More-or-less inviting yourself is not necessarily different than a non-interview invited talk.)
I agree that you shouldn't reveal which of your invited talks are actually interviews, but that's only an issue if all your invited talks happen in the last semester before you submit your thesis. (And maybe you should wait until after interview season is over to add them. The people who are interviewing you are desperately curious about where else you're interviewing.)
I wouldn't say it's unethical to list them, since I think they could legitimately be considered invited talks, but I would strongly recommend leaving them out. Partly that's because it's not worth the (probably small) risk of offending someone who really doesn't think they belong there, but mainly it's because in my experience most people don't list interview talks on their CVs, so listing them will look a little unusual. In particular, it may make people wonder whether you felt you didn't have enough other talks, whether you're doing other unconventional things in your CV that they should watch out for, etc. This isn't likely to cost you a job by itself, but it's not what you want readers to be thinking about.
There's a general meta-principle here: you should make your CV look like everyone else's, not because doing it differently would be wrong, but because you don't want readers to focus on the differences.
It depends on which CV you are talking about. Hopefully you have better things to include on a one-page CV. Everything you do belongs on your "full" CV. I put departmental seminars in a different category from conference talks. I divide up my conference talks into invited and not invited (and maybe someday keynote). Interviews talks generally either go in external departmental seminars (as opposed to internal seminars) or guest lecturing depending on if it is a research talk or teaching demo. If the interview talk is only given to the search committee, then it goes under positions interviewed for and does not make the seminar list. My full CV lives on the web, but if I am asked to send a CV I purpose tailor it.