Social Cyclometer is a GPS enabled cycling computer that tracks distance travelled and feet climbed. It allows your iPhone to function as a GPS device / altimeter for capturing your cycling adventures. From your iPhone, you can post your file to Strava or send the file to yourself for uploading to Garmins or other sites. From your iPhone, you can post details about your latest ride to Facebook and/or Twitter. You can also pull up saved files on your iPhone and replay the statistics from that ride.
Continued use of GPS running in the background can dramatically decrease battery life.