Unfortunately, I quickly discovered that Nike+ requires users to purchase a tiny, proprietary sensor under the cushioned insert of compatible Nike running shoes. And as a convert to Vibram FiveFingers and barefoot running, there was no way I was going to buy a pair of running shoes -- not even the pseudo-minimalist Nike Frees.
But at long last, Apple and Nike have ditched the sensor:
[I]t just became obsolete: Nike has all but replaced it with software. Available now in the App Store, the big change in Nike+ GPS is right there in its name. The new app uses the GPS radio in compatible iDevices to track your runs and plot them on a map, and also uses the accelerometer in the iPhone to record your pace. Because it uses the accelerometer to track your steps, it also works with the iPod Touch, although no maps will be displayed as you run. You could even use it on the iPad, although you’d look pretty stupid.The reviews have been generally positive -- and it only costs $1.99, which is several hundred dollars cheaper than the Garmin Forerunner I bought (and rarely use). If you're a runner with a compatible iPod or iPhone, get thee to the App Store.