After going through several job interviews doing the whole dance and show I sent the whole thank you letter spiel about how I really wanted to work there etc. I got a few thanks responses but none of the interviews ended in an offer. Two of the thank you notes were forwarded to a HR person who responded to me to contact them directly with any questions.
After several runs with this I decided to end my next 2 interviews with a thanks for your time let me know if you want to talk further and then end it there. I never sent a thank you note. Interestingly I got offers from these 2 employers. I wonder if it was my non needy attitude.