Mine, its six months. And because it is heavily used day in and out, six months is already long. Normally, I brought my iPod when I hit the treadmill in the gym. And because I sweat, it seeps into the earphone; thus, affecting its sound quality. And the rubberized lining around the earbud fades as time goes by.
My only complain is that the original earphones–the one that is free when you buy your new iPod–is just hard to look for. And they are way expensive.
Better take good care of this new replacement if that’s the case. I just have to make it last for at least a year.