during my course as a nursing student in school, i found that most patients didnt take the time to say thank you to the nurse. patients have absolutely no idea how hard their nurse (well, most of them, at least. there are always the bad apples) work for them. i had a patient once who made it a point to thank her nurses and her doctors and it was such a breath of fresh air.
on the other side of the coin, i am always careful to say thank you and smile towards waiters/waitresses, mailmen, sanitation workers etc. a thank you goes a long way.