I understand the whole gaming of system issue. How about a compromise- averaging a particular year/make/model of a car together and then being able to sort by that. You could have a minimum amount of cars before doing the average (or just list how many cars go into making the average listed beside the average), and maybe throwing out the high and low. That way the car becomes the star and not the users who drive it. That takes away any competition. Then users can click on the average beside a car and see the individual users that make up that average.
Another way to highlight individual users and high mpg is to base the top mpg not just on what the user reports, but how long they have been a member of Fuelly. That might discourage someone who just shows up and says they get 1000 mpg for a car. They wouldn't show up at the top of the heap because they just joined. You could also take into account how many fuel-ups that have added.
On the basis of a users time on Fuelly, and the number of fill ups that user has had, and how relatively close (Say within a few percentage points) of what the MPA states, I can see how this would easily defeat the gaming system. On top of that, after a few more months of users adding to their fill ups, if someone does start to game the system, it'd be obvious and admins can easily be notified of the gaming, then drop the gamerz on ACCESS IS DENIED page, their stats are never shown, their email is black listed, etc, etc, etc.
Thanks (I actually did look at the FAQ; clearly not very closely) - I didn't even realize that "incentives" were a part of the site. The methods described by "mattb" and "Pontiac" would certainly help to alleviate gaming issues.
As more users become involved and more data is collected, I hope to see statistics that sort by best fuel economy.