Apple's new slogan for the iPod nano is perhaps the best way to describe it. I dropped by my local Apple store this morning and they had a few for display (didn't even ask if they had any in stock :-)
It weighs almost nothing - almost lighter than the USB flash drive I had in my pocket, and by comparison makes the iPod mini look huge. Even the Motorola RAZR V3 is thicker; the dock connector at the bottom is literally the thickness of the entire device. The screen is surprisingly bright and sharp. The controls and interface are smaller but otherwise identical to the iPod photo. Despite its size, it seemed solidly built and I could see keeping it in my pocket without worrying too much about breaking it. The only odd design element I found was the headphone port is on the bottom, rather than the top like the other iPods. I suppose this is because they couldn't fit an LCD and an audio connector in the same spot, but considering the thing is so small it doesn't really matter which end you have to plug in.
Amazing little device - Apple will no doubt sell a lot of them!