Due to overwhelming positive feedback from Mark, David, Rob and Joel Johnson I decided to buy an 11″ Mac Book Air. I love it but it just felt like I was going to destroy it, shoving it into my travel bag without a case — the Air isn't delicate but I wouldn't call it a rugged machine.
So I bought a Twelve South BookBook, hardback leather-bound imitation book case. It is lovely. It feels wonderful, the texture of the leather is really nice. It feels to be the high-quality I'd expect when spending $80 on a laptop case. Most importantly, it feels like the Air can really take a beating if it's inside this case. I no longer fear the TSA.
The only warnings I have about it would be that the zipper does ride a bit high and can make getting USB and other plugs (like power) in a bit of a task. Sometimes the mag-safe power adaptor gets pushed out by the zipper. I"m pretty sure that, over time, the zipper will get used to being pushed down and these issues will cease.