This app is exactly what Ive been looking for. As a small business owner, I wanted an app I could start when I leave my office and turn off when I get back that would use GPS to track my mileage. This does just that, and, according to my cars odometer, its accurate. It takes some figuring out, but you can enter the details of your trip if you select "Save with Details." Then you can export your data to a *.csv file.
Is this Dawn taken? about Odometer+