The size is accurate-I wear a size 8 shoe and the medium fits perfectly. I love the arch support to keep the sock in place. I wear these as everyday socks-they aren't too thick for my regular shoes and they breathe well.
I love SmartWool socks, in general, but these don't really seem the same. They are okay, but they pill up terribly in the wash, and don't seem to breathe as well as other SmartWools I own. As usual, though they fit well and are comfortable. They seem like they will last, too.