For nearly a year, now, I've been trying to jot down the mileage on my Civic the first time I got into it each day. I started this trying to decide how much a Volt would help me get off fossil fuel. (Yes, I was a Volt fan a year ago.) Over time the spreadsheet I developed out of that plus gasoline purchase records helped me analyze the relative advantages of Civic, Prius, Volt, and LEAF for my own driving patterns.
There were a number of times that I got too rushed, or forgot to make a notation, but I took that as equivalent to being too rushed or forgetting to plug in at night. I may try to continue this when I get my LEAF, but it seems as though I'll need to record not only mileage but also "fuel intake" (i.e. kWh) each day. I'd love to be pleasantly surprised, but I doubt if the LEAF itself will maintain a log I could use for that purpose. I expect to do nearly all of my charging at home, and all of that at 120v, so my current plan is to connect through a "Kill A Watt" that I have. I fear, however, that writing down two numbers from two different locations every day is going to get old real fast.
Something that seems barely possible, and would be really neat, would be if I could use CARWINGS to query mileage and power intake from my computer. Then I could set up an autorun program to emulate web browser commands, run it at the same time every day, and log the results.