I don't remember ever doing it when I was young - My sister does it currently for her daughter's teachers. Her daughter has medical issues, so the teachers do sometimes have to do an awful lot more for her daughter though.

I did get a note from my 4th grade teacher recently (my niece had just started at my old elementary school and ran into my 4th grade teacher), so it was awfully nice being remembered. I emailed her. She was quite happy I'd remembered her and how much I remembered of her class.