@Sneakers41 - Wow, that is a lot of interviews. I wanted to add that I think that body language does say a lot about the candidate and so do thank you letters.
It is really important to send a thank you note to your interviewer immediately after your interview. It demonstrates that you are polite and notice small details like this. It also helps to keep you in the mind of the interviewer so you are more likely to progress to the next stage of the interview process.
Anything that you can do to set yourself apart from the rest is important and will raise your chances of getting the job. I worked in the staffing industry for many years and these were the interview tips I would give my applicants.
Following up after the interview is important because that is the exact time that the employers are deciding who to bring back for a second interview.