Hey, BHS. Even if you don't hear the difference, you'll definitely hear it once you're able to afford some gear that are higher-end than what you might have now. With some quality headphones, a lot of people notice the difference. There's no way of knowing when you might be able to purchase some equipment that will let you hear the difference, but the safest bet is protecting your music, which you can do now. Which means storing all digital files as lossless (Apple Lossless or FLAC, or WAV or AIFF files.) That way, you'll be sure that when you can eventually hear the difference, you won't kick yourself for having spent a small fortune on crappy lossy files bought from iTunes store. B/C if that happens, you'll want to buy the same music over again. Not good. If I were you, I'd go to a local used CD store or something, or save $ for the special recordings you really want to get, and get the CDs, store the files in lossless. Or go to digital music sites that offer high-rez files. Try to keep it at 320 kbps at the very least.

It also depends on the type of music that has been recorded. Certain things - a sustained flute tone, a female vocal with light accompaniment, etc. - can more easily reveal the differences in MP3 encoding. Other music can make it harder to hear.

Even less expensive headphones can be quite revealing of the differences. Additionally once you learn what to listen for you will hear the differences more easily