I have just completed an interview, and sent a thank you email to the hiring manager and the president of the company. They were both in the interview. If I have a second interview, do I send another thank you email/letter? Also, If they offer me a job do I send another thank you letter? How long after each should I wait to send the letter? Should I expect a response from any of the thank you letters? All of the interviews have and will be in person.
I have been on both sides of the equation. Over the last thirty years, I have been called to approximately 40-50 interviews with both recruiters and hiring managers. I have also interviewed 20-25 candidates, both individually and as part of a panel. I have never sent a Thank-You card or email, nor have I received a Thank-You card or email. That being said, I am in the IT field, where social acumen tends to not be judged as highly as technical expertise and experience.
That being said, I always personally thank the individual(s) in attendance at the close of the interview for their time and consideration. When it comes right down to it, I have always felt that the interview process is a time to seek confirmation for a decision that has tentatively been made. I tend to rely more on the presentation of the resume or CV as a better initial indicator of the potential value of the candidate. The purpose of the interview is to determine how closely the person I meet matches the person I read about. There have been situations where there was clearly a mismatch between the two--some candidates underestimated their abilities and potential value, while others leaned toward self-aggrandizement.
If sending a Thank-You card or email makes you feel good and is something you want to do, just do it. If you are asking if the gesture will tip a scale in one direction or another, I haven't heard of any instances where that was the case in the 21st century, but, then again, I haven't heard from everyone.
Like Neil T., I've been in the (IT) workforce for about 30 years. However, I have heard of situations in which a thank you letter has made the difference in getting a job. In fact, one of them was my own - the manager I went to work for told me that her opinion was that the other candidate and I were equal technically, but that my social skills - including a thank you letter - tipped the scales in my favor. However, this was the early 1990's ...
Anyway, most of what I've read about the interviewing process still encourages sending a thank you to each person with whom you interview. This is true for second interviews as well as first interviews. Sometimes this can be difficult, as getting everyone's name and email address can be tricky if you intervew with a team - especially if you meet with them all at once. Write down all their information if you can, but sometimes it's impossible. In that situation, I recommend sending the thank you to the manager (or HR representative) and asking them to relay your thanks to everyone else.
While some advice still recommends a paper thank you letter, I think an email is acceptable. This is especially true in technical fields. Unless you have something especially important - like saying you realized you misspoke and correcting that - keep the message short; this is just a thank you to (hopefully) reinforce a favorable impression, don't risk that with a long message which may annoy the recipient.
Thank yous are usually written the night after the interview. This gives you a chance to write it while things are still fresh in your mind and shows you're prompt. The evening after that may be acceptable. Be mindful of sending a message during the work day which may be perceived as doing your job hunting on your current employer's time.
If you get to the point of an offer: A brief thank you to accompany your first response, regardless of if that is an acceptance, rejection, or counter offer is appropriate. It may be most important for a counter offer, as you don't want to upset them at this stage.
Generally, I don't expect a reply from a thank you letter/email.
I do believe that sending an e-mail of thanks will help you stand out, but I would keep it extremely brief. Sending paper letters might seem a little too extremely keen / desperate - to me. One detail is to create the context for the follow up e-mail in the meeting:
Thank you for your time today. Attached is an electronic copy of the presentation we talked through during our meeting.
My contact details are below, no need to reply to this e-mail, but I hope to hear from you soon,
If you do this at each interview, you can keep saying thank you.
However a word of warning - part of the nice positive feeling you are creating is due to the "thanks" and "no need to follow up" combo. If you send a thank you with a follow up question, the interviewer suddenly has to do something. So stick to providing them with more info (electronic copy of something, links to your Stack Overflow Profile, links to your open source project, etc.), rather than asking them for more info.
According to AskAManager (http://www.askamanager.org/category/thank-you-notes), followup notes should generally be sent to everyone you interview with, using email, be brief but used to both thank them and to clarify points or ask a quick followup question, and should be sent a few hours after the interview: a long enough time to not seem desparate, but short enough so they easily remember you. You should not expect a reply.
There is a LOT of good advice there, enough that it would be hard to reproduce it all here.
Personally, I hold off on sending thanks until the end of the interview process, after I either receive a rejection or a job offer. I tend to go through the hiring manager and/or the HR representative that I'm working with at this point, thanking them and the individuals who were part of the interview process, sending a single note (typically via email). This reduces clutter in everyone's inbox (don't forget - they have other duties and responsibilities). I wouldn't expect any reply back, either - again, they are busy with other things.
During the interviewing process itself I would only send a thank you letter / email if it was to actually chase up something with the employer / clarify an aspect of the process.
There is also a context question around how many people interview you - if it's just a couple that's one thing, but if (as is often the case these days) you end up being interviewed by a dozen people over the whole process, do you really want to be remembered as the person who spammed 12 people thank you notes?
The face to face interview(s) are where the decision gets made, and I would go so far as to say that any thanks you notes prior to rejection / acceptance of an offer would be annoying for a manager, especially if dealing with high volumes of applicants. Just make sure that at every interview end with a ‘thank you for your time’ whether it’s a phone or in-person interview, and you should be covering all bases.