An expression of gratitude: said their thank-yous and departed.
Some might argue that thank-you keeps the same company as other assumed over used words like love and sorry. They have become so much a part of our day to day conversations that they have lost all meaning. It's become somewhat stylish to be complacent and unaware of other people in their lives... Or at least this has been a recent experience of mine.
The expression of gratitude is delicious for both the thank-er and the thank-ie. Think back to the last time someone give you a genuine appreciation... more then likely you did something common that you would usually do. One time I went with a friend of mine to Walmart to help him pick up stuff for a new place that he had just bought. I didn't do anything special... I just walked up and down the aisles with him and chatted- helping him to the car with some of the bags. No big deal- the next day though he sent me a wonderful little card thanking me for my company. It was sweet.
The absence of thank you can often be detected. I never find myself feeling entitled to have another person swoon in gratitude over things like I do (often going over the top when something is tasty and makes my belly happy.). I do search for some type of subtle reaction though, a sigh of contentment or an expression of enjoyment is all the appreciation I need- after that the words are just dessert (if they happen to appear).
So be aware, look at the people around you and all that they do. Tell them you are grateful for who they are and how they contribute to you life. If they are important to you then it's important for you to express that.