most hard drive failures involve head touching platter. The space between head and platter is soooo small already that it doesn't take much for it to happen. I'm amazed hard drives last as long as they do with all the head and spinning, but alas, technology. By freezing the drive, the minute shrinkage caused by the change in temperature is often enough to get the drive functional again for a short period of time. Its amazing stuff really. If you have a lot of humidity in your place though this trick could go very sour because of condensation. Our buildings here at work are dehumidified I think.