I mainly use my IPod at the gym and when travelling, but for me the gym is the toughest environment both for keeping unwanted sound out and for keeping headphones in or on. I have tried all the usual things, standard Ipod white headphones, and terrible Skull Candy ones, which stayed in but the sound transmission through the cheap cables was terrible.
I have also been very dubious about spending large amounts of money on headphones, I love my tunes but running or pushing weights in a gym is not your standard audiophile environment so took a risk on spending £50+ on these. I need'nt have worried, these are simply the best headphones I have ever used. Sound quality is fantastic, they are ultra light, incredibly comfortable and most importantly stay where they are supposed to, in your ears! They also transmit very little noise through the well shielded and not cheap cable covering, meaning there is not the sound of your every movement interferring with the music.
Excellent and if I ever need to replace, I shall just be the same again.