In reply to Newbuild100: personally I wouldn't bother. I've heard many accounts from family and friends that they are no better than standard socks. When I was working in a shop I had loads of people telling me this, one or two took up their offer regarding their "blister free guarantee".
I always found it difficult to get the creases after they had been worn a couple of times and washed.
The only time I think they may work is for blisters on the soles that are purely due to walking very long distances.
if you really want to try using double socks you could buy some coolmax liners cheaply.