That's cool. Though I'd prefer an inserted sole over a sock :-)
In my opinion the most interesting application for this sock would be to analyze where the foot performs the highest pressue on the shoe.
But I think the hardware design is very difficult, especially the electrical contacts between the sock and the device. Some heart rate monitor vendors have already switched back from fabric straps to rubber straps.
Please integrate into Run.GPS support for smart socks
I think this will be an upcoming trend, if it works reliable!
Smart Socks send fine grained information about your feet and activity via bluetooth to your mobile device. There is even a SDK. So best of all would be, integrating this into run.gps. Now that Android 4.3 supports BLE, this will be possible.