You can see my reasons for building it here: http://www.marengo-ltd.com/gps/
The actual application is here: http://www.marengo-ltd.com/map/
Feedback so far has been overwhelmingly positive. I’ll be using this blog to update you on any updates, and other comments related to it. If you are a user of the application, consider susbscribing to this site’s RSS feed. And feel free to post comments!