I'm looking forward to seeing what other participants use for their socks and how they will hold up to wear and tear. I know some knitters are using Blacker's Tamar and the Knitting Goddess's new Wensleydale and Shetland mixture. Yarns with Wensleydale and/or mohair should hold up well to the abrasion that socks go through. I've often heard that adding a strand of Rowan's Kidsilk Haze mohair yarn to the heel will make it extra strong.
I've gone stash diving and have decided to use Triskelion Yarn's Elen Sock which is 100% Blue-faced Leicester, so I know it will be soft on the feet. It has a high twist, so it should be quite durable.
Or the Winding Way socks from Tin Can Knits' book Handmade in the U.K.
The KAL doesn't end until June so I may have time to knit more than one. Joeli herself will be wearing a pair of no nylon handknit socks every day from June 11th to December 10th and documenting how they feel, wash and wear. I will be watching with great interest. I'm not a great darner, so if I go to the trouble of knitting a pair of socks, I do want them to last. I'm sure to get a great list of all-natural yarns to use for future projects out of this KAL.