Nike has released the Nike+ GPS iPhone application to help you track, map and analyze your runs. It is a paid $1.99 application. Without needing the shoes, wristband, and/or monitor, the Nike+ application uses GPS to track your runs. It is very well done and can run in the background using iOS4. It is noteworthy that Nike has decided to sell the application. The Nike+ gear (shoes, monitors, etc) can cost $100+. The application does everything the gear does... but $1.99 won't exactly make a dent in Nike's sales. You would think they would opt for mass distribution and view it as a way to promote the Nike Running line, community, and events. Furthermore, it is a relatively competitive space - some of the most popular applications are markedly more expensive (~$10) but there are free alternatively (despite having less functionality). Again, $1.99 is not priced for market share and some buyers will ask themselves if it is worth spending money after having already purchased a running app(s).
For past users of Nike+, it is a familiar interface. The app can track an entire run or guide you to a pre-determined distance or speed. Once you complete your run, you can sync it with NikeRunning.com, earn badges based on your historical performance and connect with friends.
But the best part is the mapping. Below is a heatmap from a walk to the grocery store. It shows speeds at different points and then charts against the fastest / slowest moments of the run / walk. Simple concept - but it is very well done and surprisingly very fun to use: