Gadgets don't live forever. If you're addicted to your iPod, that thought might sting a little. For an estimate into the lifespan on the Apple of your, uh, ears, there's the iPod Death Clock.
Input the serial number of your device onto iPodMechanic.com, and it will calculate an estimate. Of course, it's not totally accurate, depending on how much you use and/or abuse your iPod, it will change.
For those who don't have their serial number, they provide sample codes for iPod Video, Photo and 4th Generation.