Does "Thank You" Really Work?

As someone who tries to follow as best as he can, what he writes about, I had written a short thank you note to someone who I was really impressed with as I was in the process of updating my health insurance. What did they do that was so special? They helped me get much better insurance coverage, but in a way that really went above and beyond (I thought).

Now I'm not sure how powerful comments like these are to someone, until I get a response like this back:

"Wow! Thank you very much! I have been