In my mailbox a while back:

Just a note to say thank you. For all the times you made us turn in our reports via the computer network and slammed us for poor document formatting (i.e., using spaces instead of properly placed tabs to align info), thank you. I now preach and teach your sermon to others and improve their computer skills and efficiency. I am beginning to realize the importance of some of the little things I learned from you and other professors in the department.