eg. My YP-55 has survived being dunked fully in water, and being dropped 50+ times including a fall from my pocket while running which resulted in it tumbling along beside me on hard sidewalk pavement for about 6 feet (2 meters). It survived this partially because of its aluminum casing, internal flash drive, lack of any moving parts and a hard plastic screen. Also the dunking, being able to instantly eject the battery probably helped, along with the hair dryer (and the fact it was submerged in water for only ~2 seconds).
Not sure if you can include player lifetime here, but it has been running for over 5 years now.
Also of note is that first generation YP-55s came with a very good protective case, but one which made use of the unit quite difficult...
