I've had these headphones for around two years now and only in the last few months or so have I noticed any wear in the sound quality. However, this is not surprising as I have been less than gentle with them. They've been thrown around, dropped, stuffed in a drawer, kicked, you name it. Remarkably they still worked fine for ages. The only problem now is the jack-plug sometimes needs twisted a bit in my Ipod when I start loosing sound in one ear. I will definitely be purchasing these headphones again as for 6 pounds the sound quality is well above that price, plus they are very robust, they are the most comfortable ear buds I have worn and they're cheap enough to restock once they go the way of the dodo. I should also mention that these headphones don't use the system of looping the wire round your neck, it is the standard parallel wire which I love.
Definitely a recommended purchase, I doubt you'll find better headphones at this price.