I wear these socks daily as a liner sock under my regular socks.  Given that my feet sweat a lot, they wick the sweat away and keep my feet comfortable and dry.  They also add a little additional warmth, which is a consideration for Wisconsin winters.  I've also found that I don't wear out my normal socks as quickly; they've pretty much doubled how long it takes for holes to develop.

I also wear these socks for running with my Vibram Five Finger shoes.  They help prevent blisters (which I've experienced with my bare feet in the Five Fingers), and help keep the shoes from getting stinky.