Cardiotrainer uses the GPS in the phone to track the exact path (overlayed on Google Maps) that you jogged, biked, etc.. It shows your speed, avg speed, how long you jogged/biked, and a bunch of other stats... It even posts it to facebook when you're done with your workout (but I don't really care about that). It also tells you approximately how many calories burned based off distance, speed, etc...
Thanks