I was wondering if a plug in could be created which allows you to tell MM your average mpg and your current fuel load. When you input a new destination it could then tell you if you will need to refuel along the way and make a suggestion (based on petrol station locations) as to where.

You would only really need to set your mpg once and many modern cars have an on board computer that would tell you your current fuel level so you could be prompted for that when you set a new destination and thats it.