I use a pouch, which allows me some protection and to use the case naked... my only problem is how damn slippery it is. I'd actually be interested in putting some kind of transparent skin on the back for the purpose of grip alone but I haven't looked into it.
I went without a case for a few days, but after nearly dropping it I opted to go with the thinnest clear plastic case I could find - not so much for the protection, but really for grip. But I could tell one really doesn't even need a case with this thing. The aluminum is solid and hard to scratch.