I registered here a short while ago and I thought I'd jump into the fuel economy records with my smart.
Rather than registering the 135+ individual fills I have to date here individually, I entered the cumulative "to-date" distance (miles) and fuel used (USG). The detailed records are at spritmonitor, a German site that records mileage in L/100 km. Click on my signature's L/100 km icon if you want to see all the records.
So it's a bit under 61 US MPG, which apparently puts me into third place here, surprisingly!
I don't make too much of an effort to drive economically, and the car is not modified in any way to improve economy....in fact, the main modification is wider wheels and tires, which have the opposite effect, but they do make the roadholding a lot better than the skinny tires the car comes with. These double three spoke wheels ("strikelines") are original smart wheels, but are not available in Canada. Officially
Being a convertible, the top is often open, and so the highway fuel economy suffers as a result. But I don't care; I'm still in the first percentile for fuel economy compared to other locals. I use the heated seats and air conditioning a lot too (in fact it is fair to say that either the roof is open, or A/C is on, or the heated seats are on, or two of the above ---- but never A/C and roof at the same time).
I recently got a ScanGauge, which I am finding to be useful, but I am not going crazy trying to minimise fuel consumption. I also like the other features it has.