refurbed nano or not
I bought a brand new iPod nano last year, only to discover (when the email from Apple showed up a month later to inform me that my warranty was about to run out), that my nano had already been bought, used, returned, repacked (and the packaging was pristine!) and resold.
I totally agree that the serial number is the way to find out the true history of your nano. Apple can not only give you the definitive answer as to whether or not it is a refurb, but which vendor it was originally sold to (which is both kind of cool and creepy)
(it turns out that, although I bought my nano from a well-known, nation-wide chain store, they weren't actually "official" Apple resellers; they bought their stock from a second, or maybe third, tier distributor, just to be able to carry Apple products on their shelves. Lesson learned on my part; since Apple prices rarely vary, I now always purchase directly from the Apple store or one of the true, reputable Apple vendors out there)