Confirmed issue on skins in 14w34c on some computers. I see report of Beed28 on Minecraftforum.net :

"After updating to 14w34c, my skin is no longer working ingame. When I load the game, I either appear as the default Steve? skin or the weird abomination thing in the attached screenshot. My skin appears fine in 1.7.10."

http://www.minecraftforum.net/forums/minecraft-discussion/recent-updates-and-snapshots/2187378-my-skins-not-working-in-14w34c