I've been wondering why the case of my mac is cracked. I noticed yesterday when I put my Thule backpack down on a hard floor that there is no padding! Clunk.
To be completely fair, there's about 2mm of flimsy padding on the bottom of the laptop sleeve, which isn't enough, and if you put your laptop/ipad outside the sleeve, there is absolutely no padding on the bottom (or sides) of the backpack to protect it.
I'd already taken to keeping my mac in a plastic bag, since the Thule is not waterproof (the zips leak even though the material is said to be waterproof); I've now inserted a piece of 1cm foam to cover the bottom to provide the missing padding.