I finally bought myself the silver Apple iPod Nano, and Nike Sport Kit for my Christmas present. I've had it almost a week now, and have used it and uploaded my data on-line.
I used a little velcro pouch and placed the little transmitter in it and headed on my route. I know exactly how far the route is because I've used a GPS and measured it out. I was surprised how accurate the system is without calibrating, if you walk. When I mixed running, jogging, and walking during my tests the system was off by a lot.
I measured out a distance with the GPS and then calibrated the running kit. That helped but it seems that you'd want to get two transmitters, if you really were into the accuracy thing based on walking or running. You can buy the transmitter by itself for $19.00. Overall, it was close enough for me as long as you do the same routine.
Basically this is a fancy pedometer, multiplying the stride length * steps to get distance, and using your weight to determine calories burned.
The variations in workouts are good, distance, time, calories, etc...you can mix your playlists, random, etc...I liked that a voice would tell me my progress and then at the end (400 meters) would do a countdown, 300m, 200m, etc...I kicked in my powersong, during the last 200 meters for that final kick. :)
If I made a new time, or record, distance or other milestone, I was congratulated. I uploaded my info to nike plus. There, a flash chart shows all your runs, and progress to share or keep private. For $29.99, it's a great motivator!