Today when I took my air 13 out of bag, I accidentally hit it against the shelf (made of metal) above my desk. I was so pissed off when I heard the huge bumping sound. However, I only saw a tiny dent which is only visible at certain angles and no skin came off. I was a little surprised because skin of my 2005 AL powerbook came off in some spots even without bumping after several years of use. Maybe apple improved the skin anodization process.