I take pretty good care of my nano - no keys, no pocketchange to sit with the nano in the pocket. All scratches have been made by the plastic earbud headphones. It's almost a given to have to tuck the nano in with the headphones in the same pocket when not in use, unless if I want to unplug the headphones and put them into separate pockets.
In my opinion, I think that there's something seriously wrong if I need to buy a protective sleeve in order to prevent irreversable cosmetic damage to a $250 music player during normal use in under a day. I had always been under the impression that the sleeves were for more trying users, who maybe wanted to subject their ipods to coins, keys, or the elements - not for everyday use and sitting in a pocket while I listen to a class lecture.
I front pocket the nano, spray it down with iKlear constantly to get rid of fingerprints, never jog with it when the earphones are coiled up with it in my pocket, never keep it in the same pocket as the cellphone, never keep it with keys or coins, and have only 'abused' it by having it rest in my front pocket with the apple earphones while I sit in class. And I'm a guy, so these aren't exactly tight pants either. I would say that the average customer doesn't take care of their nano as well as I do, and I had mine showing mild scratching in a day. That'd be like driving around in your new Honda, and having the paint begin peeling off in a day, unless if you bought a special "paint protector." Add to the analogy that Honda doesn't tell you that your paint's going to peel off in a day without the protector, because every other car you've used has never had the same problem.(At least of the same degree.) And, say that one of the big selling points of the car was how sleek it looked.
Actual functional durability hasn't had a single issue. I'm pretty sure that this thing can take a lickin' before it breaks. It's just that after about two weeks of normal use, it'll look as if you threw it from a speeding car. (Although I still wouldn't do it anyways, even though it's been tested to resist damage.) Wouldn't let that deter anyone from buying a nano, although I'm going to have to keep an eye on the LCD from what Jesus posted...