Have you seen this?
Go to the products section at Nike+ to check it out.
Basically, you need Nike+ ready shoes, the Nike+ software and an iPod Nano. You sync up your shoes with your Nano... it keeps track of your miles, calories, etc... and when you sync your Nano, you can actually compete / challenge / communicate with other Nike+ participants all over the world. It even talks to you when you run / walk. Nice.
Wish I'd have thought of it!
Now I want it.