My son, Mark has one of those Nike sensors in his shoes that record his running and send the data to his iPhone. I've got a Polar watch that communicates with a band on my chest recording heart rate. The treadmills at the club can receive the data from the Polar watch. I haven't used it for a couple of years because the battery is dead. I'm going to have to send it back to Polar to get it replaced since the watch is sealed.
I've also looked at new wrist sensors such as the Nike Fuel Band and Jawbones Up. So I do understand some of the special things a smart device on your wrist could do. Tog has a lot of examples in his article.