The Giving Notes (2012) by Heo Chang-Gong

Materials: ABS, PVC, paper

The Giving Notes is a sticky memo pad that is shaped as the trunk of a tree. It is playful showing the essence of paper as it is. As the memo pad is used, the trunk of the tree will gradually disappear. Sending messages of the effects of wasting paper. So the more it is used, the more trees will disappear. 'The Giving Notes' will be donating part of their proceeds to planting trees.

EDIT: A couple of people wanted to know where one could buy this product. You can actually buy it here, and if you want to stock up on refills, go here.