My MacBook Air case is a Ziploc baggie

I bought the 11" Air instead of the 13" because I wanted portability above all. It's a tough call, but Lion's 'full screen' integration with Mission Control makes that small display usable. For real work, of course, I add an external display.

So I didn't want to sacrifice portability by adding on a $30+ neoprene sleeve. The Air itself feels pretty study. It is, however, not waterproof. So I've been looking for a tight fitting 'case' that would provide water protection with a bit of surface protection.

Something like a .... baggie (I know what you were thinking).

For the moment I'm using the Ziploc 2 gallon Heavy Duty freezer bag: 13" x 15.6". The horizontal (13") dimension is a good fit, but it's far too long. I would prefer a 13" x 8" baggie. So I'm still looking, but for the moment the current bags are fine. Those I don't use up on the Air I use in the kitchen. The price is certainly right.