A few of us at Giz debated this for awhile, but using it while on the road for a month made me sure that that the new nano's case is too sharp on the corners, compared to the old chubby one.
I prefer the old one by far, because it is shaped with both impressive lines and curves, like any nice modern automobile, but more importantly, it feels both smooth and slightly "edgy" in the hand. The modern Nano leaves with the impression that its shape is a result of a very simple manufacturing system, not really designed to fit a person's hand first and foremost. I picture it being made by taking a long piece of aluminium, extruding/cutting out the middle to form an oval, and cutting off the proper lengths. The corners end up being very sharp, and putting it in my pocket, I can feel my pants wearing down, and while holding it in my hands, its definitely poking into my palms in a not nice way. And you never get over the jarring feeling when holding it in your hands. The curved screen is neat, but it picks up glare. And not just regular glare but glare like that in a funhouse mirror, which is slightly more distracting than regular glare. I'm sure its cheaper to make the case, but I prefer the case of the old one better. I even like holding the fat Nano in portrait better to watch videos. So why not buy an older one? Because the new one has a far superior menu system and you can shuffle to the next song by shaking it. Design goes beyond just the form factor. [iPod Nano Review]