Mine has got it too. I saw its birth from the corner of the usb port, its day-to day growing and its death onto the earphone slot after a few days.
Probably it's due to a too sharp curve of the usb port that stress the material too much. Mine never fallen, ever threated with care, never brought with me away, always used at home, never hurted anything.
It really seems a design flaw never noticed by Nokia, probably only a 'rounding' of the hole for the usb port will be enough to prevent it to start.
(qutoe)A little flaw in a great device(/quote)