I used to think they were a massively overpriced fashion accessory bought only by people who were brainwashed by the never ending repetitive video being shown in most outdoor shops (pity the staff who had to put up with that all day) - then we all got one 'free' at the Ben one year and since then I'm convinced.
Still think they are overpriced though - lots of much cheaper copies out there nowadays and somebody kindly posted a link on here a bit back where you got three for next to nothing. I haven't 'lost' any of mine yet but they keep moving in to different jacket pockets and bumbags spontaneously.
I lost one once. I viewed a clubmate with suspicion who had started wearing an identical one. They're so good I eventually had to buy another. Then the original turned up at the back of a cupboard! I now have two buffs.