Question: When are your earphones no longer earphones?
Answer: When others can hear your music too.
How deaf must you be if I am sitting 6 rows behind you on the train and I can hear your music playing? Not only playing, mind you, but also able to recognize the song and actually hear the words? Above the noise of the train, no less? How can you possibly be enjoying what you hear?
I can't understand spending a few hundred dollars on iPods and high-quality mp3 players only to louse them up with sucky earphones. Earphones are like a fine tuxedo, running shoes, or a quality bra - you gotta try a few on and be fitted (I am only guessing about the bra part but it does make sense). All earphones are not built for everybody. We all have different shaped heads and ears. So just pulling a random pair of Sony, Panasonic or Sharp earphones off the rack at Best Buy does not mean they will fit your head, or even into your ears. Ask the salesperson to let you try a few sets out. I did, and they did. They already have them open and will let you test them out before you buy.
It's worth the time and the investment. For everyone. After all, it is YOUR music.