One of the great things (maybe the greatest thing, actually) about the Nano is it’s compact size. 3.5" x 1.6" x 0.27" and 1.5 ounces is pretty tiny for what it does. It’s easy to slap this thing in a pocket or purse or hang it around your neck while you’re listening to your tunes. The OtterBox, while terrific at keeping your Nano safe, isn’t exactly svelte, however. It measures a noticeably larger 5.125"x 2.25"x 1.00" — about the same width but an inch taller and ¾ inch thicker than a 60GB iPod with video sans any case. Clearly this is not a case for anyone who is conscious of their iPod’s size or wants their case to be a fashion accessory.
As far as weight is concerned, again the OtterBox adds a noticeable (although IMO negligible) amount of weight, and I suspect the additional weight would be less evident with the models for the larger iPods.
As I mentioned before, I have a 4th gen iPod, so the size and weight really wasn’t an issue for me. My wife’s Nano didn’t seem too large since I’m already used to a bigger form factor. And interestingly, the OtterBoxes for the rest of the iPod family really aren’t that much bigger than the Nano case. So if you have a bigger iPod like mine (or the new iPod with video), you won’t notice the size hit nearly as much. To be clear, they are bigger than a form-fitting case, but if you need the protection they are worth it.
For my wife, however, the size of the Nano holds much of its appeal, and she felt the case was too bulky for her needs. Something to keep in mind if you have a Nano or Shuffle and don’t specifically need the armor plating offered by the OtterBox.