That's an incredible idea. I really wish it was available a desktop application though. Such an app could gather information from multiple sources (including companion mobile apps) and maybe even location-aware social networks. It's useful on a mobile phone but i would rather buy a dedicated gps device to track my progress as constant usage of gps on a phone will definitely decrease it's battery life. Also I really feel uncomfortable handling this kind of historical data to any sort of SaaS. I would definitely pay as high as $10 (or maybe even more) for something like that.