Any time you have an intricate piece of machinery, you'll need replacement parts. It's no different with an ear phone. The most common replacement parts include jacks, cables, and ear pads, all of which can become disconnected from the headset with excessive use. If you just own a cheap set, you could probably buy a new better sounding set for less money than the replacement parts. But if you are a serious audiophile and you want serious sound, you'll also want some replacement parts just in case the music makes you dance too hard!
Lastly, consider getting some rubber alcohol or cleaning solution to keep everything sanitary. After all, they are around your ears and your hair for a long period of time and they can get a little grimy and wax can build up in your stereo in ear headphones after excessive use. Keep them clean and you'll enjoy them more besides getter better sound from wax buildup.
Protect your teenagers hearing with a quality set of stereo Black Pods pro for their Ipod.