Depends on the interviewer. I've had some interviewers to whom I've sent a thank you note and left it at that. It would just alienate them, I think, to get an e-mail. I've had another interviewer, though, who made it a point to give me his business card (we were down the hall after the interview and he made us walk back to get it) and who told me to e-mail him with any questions, concerns etc. I dropped him a line a couple of days later to send him a copy of an article I knew he would be interested in. He wrote me back a long message and we have kept in touch sporadically since then. The reason I could send him an e-mail, though, was that he liked me and welcomed it and told me so. You also should know that I got accepted a week after my interview, so all but one or two of these e-mails have not been about acceptance, but about other topics (books to get, political discussions, families, etc).