i have an Incase sleeve for my MacBook Pro , and use a regular backpack... in my eyes the sleeve prevents scratches from pens, paper clips, spiral notebooks, etc when in the bag.
I'll be getting the Incase shell for the MBP soon too, this would help prevent dents when I have those moments in where it slips my mind that a $2000 laptop is in my bag, and I place it carelessly on surfaces
i've seen that backpack at the apple store, and its a little on the big side for me to be on my back... but no matter what Incase makes some good products for MacBooks & MBPs
DJ Asian Sensation