I just purchased the air 11.6 and searched the web like crazy trying to find a thin neoprene case so I can fit it in a purse. Also searched all the office stores.
Tonight at Wal Mart I found one that fits very nicely! It is the SwissGear 10.2 Lunar computer sleeve. It's black and has a zipper pocket on the front, which I don't really need, but it doesn't create extra thickness either, so it's OK.
http://www.walmart.com/ip/SwissGear-Lunar-10.2-Sleeve-Black/14964986
While it's called the "10.2" Lunar sleeve, here are the real dimensions (in inches), as printed on the packaging:
Computer pocket: 10.5 L by 1.5 W by 7.75 H
Exterior dimensions: 12 L by 1.25 W by 9 H
It is snug as you put the computer in the sleeve, but not so snug that it's difficult to take in and out. And I'm sure it will loosen up very quickly. It's not so tight that the zipper could scratch the metal; just snug. It is made for a netbook, but because it's more square than oval around the corners, it enables the 11.6-inch Air to fit, whereas other netbook cases won't because the corners curve too much.
The actual height of the sleeve is a touch higher than it needs to be, but not really noticeable. I am thrilled that I found this, because it doesn't sound like anything is in the works from Case Logic (InCase) in the near future. That is what I had been searching for, but this sleeve from SwissGear fills the bill very nicely!