Maureen Dempsey has written an interesting article about job interviews for Fast Company. She aims to debunk five key myths about the factors that drive success in the job application process. While I don't agree with all her points, I think she makes a very strong argument about thank you notes after an interview. Here's an excerpt:
Rather than simply thanking hiring managers for their time—something that doesn’t add value to the decision-making process—Hawley says to make sure your note contains meaningful information that proves you were paying attention and are still interested in the position. "Think about the conversation, and write something both personal and business-related," she suggests. "Tell them how much you appreciated discussing a certain business topic, then thank them for sharing their insights about something personal."
I would agree wholeheartedly on this point. Be specific in the thank you note. Show that you listened to the interviewer, that you learned something new about the company. What should you not do? Try to make an expanded case for why you should get the job. You don't want to be writing a long novel. However, you can express your continued interest in the job. If specific concerns arose during the interview process about your qualifications, you could politely offer to provide evidence to address those questions. In a recent interview situation, my colleagues and I were incredibly impressed with a candidate who very politely offered some additional evidence that was quite compelling. However, the person was concise and to the point, and most of all, expressed gratitude for the opportunity to compete for the position.