I've had my iPod for about two years. The nice thing about iPods is that they keep track of the number of times a song has been played all the way through, which lets you estimate the total amount of time that it has been operating (since, you know, I require data). This is always an underestimate since it doesn't register a playcount if you don't play the song to the end.
Multiplying the length of each song by its playcount, and summing, my iPod has seen 3844 hours of operation, 160.2 days. So, over the past two years, it has been playing songs at least 22% of the time. And it's still fine. It has been up and down the East coast of the US, to Italy and even to the desolate plains of Ohio and is still working just like it should.