I've got both an iPod (fifth generation, 60Gb) and a Creative Zen Xtra (40Gb). Sound quality, they're comparable, but the iPod, due to its AAC encoding, is much closer to the original music (mp3 is far inferior to AAC). But, for ease of use, the iPod blows it out of the water. It's got five buttons, a wheel, and a hold switch. My Zen has a clumsy thumb wheel, play, forward, back, volume up/down, on/off/hold.. anyhow, it's a pain in the neck to use it.
Anyhow, I love my iPod.. I even practice with it (BTW: those Shure and Etymotic earbuds you're talking about - I've got a pair of Panasonic sound cancelling earbuds.. they sound *great*, reduce outside noise by about 25db, and only cost $30) and you're right, it's really hard to hear even your own break. Kind of a different perspective on the game..
But, reading some earlier comments (such as, what if my opponent can't hear me call foul, push, hit, pocket...etc..).. Are you suggesting that someone who's hearing impaired shouldn't be allowed to play?