I do, BM, it was a ritual after Christmas (and double for me with my birthday in the same week). My brother's children never wrote. We have another younger relative who has still not thanked us for their wedding present and 2 children's new baby gifts. They ain't getting any more - even an email or text would have sufficed. Everyone who gave us wedding presents got a thank you note - if I can do it, why can't they? It's manners!
However - not everyone does it - my ex MIL thought it very odd when I wrote to thank her for presents, she told me not to do it again.