I have to manually log when I use my car for work. At the end of the year I total up my "work" mileage as a percentage of total mileage and I can claim that percentage of all of my car costs (gas, insurance, repairs, etc) as a work expense. So if if turns out 15% of all my mileage for the year was for work related driving, I can claim 15% of car costs as a work expense. What I'd love to see is an App where I can enter my initial Odometer reading and then I can create events that have a label (eg: "Trip to ABC Client Inc.") and a category (eg: "Work). For this event, I'll be able to enter the odometer reading at that time. When the trip is over, I enter the new Odometer reading. The App will log how much of my mileage is used for these events and categories. It would also store it in a data file (.csv or other) which can be exported to a spreadsheet (using Finder or SFTP). All odometer readings and trips would also be tracked by date so I could see weekly/monthly/yearly statistics. While not a very glamorous application, I think it would be very useful for myself and a lot of others out there. When I get some spare time I might take a crack at implementing this, but if any of the devs out there think this would be useful, I would love to see it!