Do you send enough "Thank You" notes?

I was impressed recently, by my brother's fiance. She held Christmas dinner at her house for the whole family of about 30 people. She asked me to bring a salad. Three days after the dinner, I received a thank you note in the mail for bringing salad. Now here's a woman with three girls, she's an emergency room nurse, she's planning her wedding on January 1st, hosting a large dinner, and she