While the iPhone has GPS, and it's good enough for most people, performance-oriented athletes may find the precision lacking. Enter EpicSesh, makers of the Xensr line of "sports motion-sensing devices." While it looks like the sensors are still undergoing testing, the promise is that athletes will get more accurate data to help training. If you've ever wanted more accuracy than that blue circle allows, Xensr is what you've been looking for.
If you're a bicyclist, you can precisely track your rides to see where you slowed down. Windsurfing, snowboarding, skateboarding and others can also track their precise movements to see what works and what doesn't. The Xensr records the full range of 3D movement very precisely. Even if you're not a performance athlete and just want to improve your times, Xensr is a promising technology I can't wait to see made available.
Until then, learn more about the Xensr from one of its creators, David Troup in this episode of Origin Stories.