What are your trying to protect it from and how hard are you on your computers?
Most of my notebook computers are like new when I replace them (after 1-3 years) and all I usually do is put them in a basic nylon computer bag or sleeve when transporting them outside. Around home, or hotel, or work I don't usually use a skin or sleeve or case.
I know other folks that tend to quickly end up with dings or scratches if they don't use additional protection. Skins are "always on" and great for protecting against scratches but can be difficult to put on and don't protect against drops or dings. Sleeves are good for scratches but are not always on and usually offer only a little more drop or ding protection. Full cases protect better against drops and dings but add a lot of bulk.
I love the Incipio Orion sleeves for my MBA 13 and hope they come out with one for the 11.6. I tried an SFbags suede sleeve for the 11.6 and while its better than nothing, its only redeeming feature is that its currently available.
Right now just using a very thin and light 13" Incase nylon bag I used to use for my 13" uMB and iPad. Will likely get something a bit smaller when it becomes available.