Post interview thank you note or not?

[PhDchallenger]

Is it over the top to send a thank you after the interview day or will it be something that positively impact my chances? Any suggestions for content?

[b_l91]

Always send a quick thank you note! Doesn't have to be elaborate or hand written, but you should convey how much you appreciated the opportunity to talk and maybe a couple of specific things that stood out to you (e.g., current research projects, mentor style, etc.) and reiterate your interest/match. I'm not sure that it will necessarily increase your chances, but it's pretty standard to do so and not doing so may be more noticeable. If you stayed with a graduate student host, it's also important to send them a quick thank you email as well.

[TakeruK]

It's not over the top but it will also not really affect your chances. It's just polite to do so.

[kitcassidance]

I think it's also a good place to briefly clarify any misspeaks from your interview.  I flubbed an answer at an interview Friday, and in a very short thank you note mentioned that I'd thought about our conversation further, and wanted to emphasize xyz.  Don't go overboard, but it was a good place for me to better articulate what I had failed to say in person.  Just got a very positive response back, with several follow up questions - had I not sent a thank you, there would not have really been a place to extend our conversation.  
(Obviously, if the conversation went really well and you have nothing to clarify, that's better news haha!)  As others have said though, sending a thank you is a nice way to bookend the application process.