Personally, I like MPG because it makes the range-on-a-tank-of-fuel calculation much easier, and I care much more about range than about fuel economy.
I was sad when it turned out the original Honda Insight didn't get 70MPG, because, otherwise, it would have been interesting due to the 700 mile range.
If we're talking about serious off-road vehicles, then I can see why you'd want to max out your range to make trip planning easier. But thinking of the majority of drivers doing the majority of their driving (especially in cars like a Honda Insight), they'd be hard-pressed to end up going somewhere that didn't have a gas station at least every 200 miles.
The first is commuting. Filling up takes an extra 5-10 minutes above and beyond the fuel dispensing time (assuming that's linear, which, with my CNG car, it isn't, but that's another topic). A car with a 450 mile range over one with a 225 mile range would save me 4-8 hours per year.
The second is pleasure travel. Sure, the nearest fueling facility may be under 50 miles away, but it may easily be 10-30% more expensive than a farther one, especially across a tax jurisdiction border (especially Canada/US). At $3/G and 60G for a 2000 mile round trip, I'd prefer to keep the Andy Jackson or Uly Grant (Common Loon or Snowy Owl on the reverse if North of the border) or spend the money on an unplanned couple hundred miles' detour.
The way I do it is that I know my work commute is about 30KM, so about 150KM per week, and that my Mazda has an average combined fuel efficiency of about 7L/100KM - meaning that my commute uses about 42L of fuel per month. I know that gas costs around $0.96/L in this area at this time of year, so my commuting costs about $40 per month in fuel.
I use this line in my budget, and hence pay less attention to exactly when I refill my tank - and know that any amounts I spend on gas above this number are somewhat discretionary.
The average person is pretty bad at dealing with fractions, too. Are they going to get the difference between 0.05 gpm and 0.04 gpm? Seems pretty small, it's just 0.01!
Another interesting argument, although I can't find a source offhand, was to force manufacturers to display a gallons/10,000mi - on the basis that since the average American drives something like 10Kmi per year, this would convey much more concretely the longer-term difference between fuel consumption.
The follow-up problem is that average person think miles per gallon is linear (as they would phrase it, "the difference between 1MPG and 2MPG is the same as the difference between 60MPG and 61MPG") because they don't know any better, whereas it's really an inverse/reciprocal relationship.
I wrote a more though explanation of this - http://www.daniellanger.com/blog/2009/08/miles-per-gallon-vs... - the last time MPG came up in discussion, when there was some minor outrage over the Volt claiming 230MPG.