I worked in the search business for what often seemed like 100 years (in fact, it was 44).
In the good old days, people would mail resumes to companies on great looking parchment paper with a watermark visible to the reader because that meant class!
After an interview, they would send a thank you note (by mail) on either personal letterhead or a card to express their interest in the job.
Now in this mile a second world, thank you notes have disappeared from proper interview behavior and that is a tactical mistake.
Sending a thank you email after an interview accomplishes several things. First and foremost, it leaves little doubt about your interest in the opportunity being discussed . . . and, in a lot of situations, breaking the logjam by expressing interest can be enough to separate you from the pack.
But probably more important is that it gives you an opportunity to (a) address any concerns the interviewer might have about your experience, (b) correct an answer you missed on and (c) give you another opportunity to sell yourself to the interviewer.
So, to be clear, I’m not suggesting that you mail a thank you note; I’m suggesting that you email one within 12 hours of your interview.