My iPod's put on weight. It's got a slight bulge on the left hand side: the metal back has come away from the white plastic front very slightly. It's not just bent, as it doesn't seem to push back into place (and I don't remember my iPod getting any particular abuse).
I'm not too worried, it's coming up to two and a half years old, and it's a 3rd gen model, so lots of room for upgrades (speaking of which, why don't Apple update the software on the old models?). Either way, it's still working fine (battery life is down a bit, but not yet a problem for me). I've been buying a bit of new music too ;-)