Neither Matt nor I are big Facebook fans so we haven't been very motivated to do this. We've looked into developing an app for Facebook, but the time involved to do it didn't seem worth the value we'd get out of it. But I know people disagree on this, and we've had several discussions about Facebook here in the forums.
If you want to import your fuel-ups to Facebook so your friends can see your fuel-ups, you should be able to follow the instructions here.
I understand that people wouldn't like fb but it would show others that we are conscious of the fuel we use and how your site gives another way of focusing on it and comparing to others with the same car as us. Also those shopping for cars can see what a vehicle gets in real world mileage. I love that.