A colleague, fan of mountain biking, found a good way to interest me to his week-end expeditions: MotionBased.com.
Simply put: use a decent GPS, record your trip, upload your data and share it with the community. Bonus includes minute by minute tracking on Google Maps, along with elevation, speed, and even heart beat. Works from simple walks around the block to long lasting road biking, or, why not, even canoe, skiing, or a bunch of other stuff... someone could even think of street racing... Knowing you can take someone else's trip and try to beat it, this will certainly happen eventually!
While some argue the speed of innovation is slowing down, what we see in this Web 2.0 wave is often new and innovative ways of using existing technologies. I think MotionBased is a very good example of several Web 2.0 concepts: community focus, innovative use of technology, Web as a platform, innovative design, etc.
Check out their demo: http://www.motionbased.com/info/product/demo/slide1.htm