I sent my favorite professor from college a letter a few years ago letting him know how important he was to me and how much he influenced me. I thanked him for setting such a great example for me to follow of what a professor should be.

He passed away earlier this year and his wife made a point of coming to talk to me after the memorial service to let me know how much he had appreciated that letter.

Now, mind you, about six years earlier I wrote letters and did the whole bit to make sure he won an important teaching award at the school and insisted he come to the ceremony for it, but she said that letter was more important to him.

I know it's not quite customer service, but there you are.