I just recently downloaded the Nike+ app after a receiving a discounted offer.
I run regularly so I was really interested to see how well this would map my runs. I have to say it has added so much to my workouts. I can see exactly how far I have ran. It tells me my average time and also maps my low speeds and fast speeds.
You don't need any extra hardware. You just need the app on your phone and as you hit the pavement , you just start up the app. It announces each mile marker and your pace for that mile as you run , which I have to say was a bit disconcerting until I got used to it. Then when you get home you can look back at that run plus all other runs that it stores in history.
Now if only I had remembered to start the app during my recent ski trip.