Average MPG
 

Most people will probably find this to be a useless feature, but I think it'd be cool to be able to see my personal average MPG, calculated as total miles driven across all of my vehicles divided by total gas consumed. It would also be nice to use this to calculate a total carbon footprint, although not sure if that would require the ability to specify grade of fuel used.

I think this is a pretty fun idea since I drive a guzzler and a motorcycle.