I would love to see an output of the databse to a see sort of ALL cars in descending order of average mpg. with filters of US owners (or British or European) and model year. So, for example, I would be able to see what 2011 US cars got the best mileage as reported by their owners.
So the sort order would be something like by Country of Ownership, model year, mpg, then model (not manufacturer).
I agree that it'd be powerful, but we feel like it would ruin reporting. We have a FAQ about it here: Why don't you list everything in order of best fuel economy?. Once you set up a list like that it turns Fuelly into a game that people can win. With that incentive, suddenly the numbers you see would be suspect. We'd rather have accurate numbers and a less useful site than completely unreliable numbers. That would make the site useless.