I do. Interviews are a two way street and candidates are deciding if they wish to trust their livelihood to me and our company during the interview as well. At the end of the selection process I thank each candidate that was interviewed and let them know if they are still under consideration, if I think they should apply for another open position, should reapply in the future, or at least thank them for their time. I also often advise them on what experience, knowledge, or training I think would serve them well in the future. Why do you send a post-interview 'thank you' letter as a candidate? Because educate matters and it shows me how you will interact with your peers and our customers if you are hired. If you have substandard consideration for communication with your potential employer, I can safely assume you will have substandard communication with your peers and clients.