iPod nano 1st (left) & 5th (right) generation models

Thanks to PC World for noting this one...

Apple Acknowledges IPod Nano Overheating in Support Doc

If you have a 1st generation iPod nano like the one pictured in the photo above (left), check uot this Apple support item...

iPod nano (1st generation): Rare cases of battery overheating

Apple has determined that in very rare cases, batteries in the iPod nano (1st generation) sold between September 2005 and December 2006, may overheat and prevent the iPod nano from working and deform it.

Apple has received very few reports of such incidents, and the issue has been traced to a single battery supplier. Additionally, there have been no reports of such incidents with any other iPod nano model. If your battery shows signs of overheating, such as discoloration or deformity, stop using the iPod nano immediately and contact AppleCare as soon as possible for further assistance.