I've noticed that my fuel gauge and distance-to-empty aren't very accurate. The gauge falls quite quickly to the 1/4 mark, then stays there for a rather long time and starts falling again at a slower rate. Yesterday I ran the car until it showed 60km distance-to-empty and when I filled at the gas station I could fit only 44L petrol. I found this TSB: http://www.underhoodservice.com/ford-focus-fuel-gauge/ Has anyone else experienced this? I don't have any of the DTCs. 

I have always thought the gauge to be inaccurate on every car I have had - it stays on full for the first 50 miles then drops quickly to about half way, then drops more slowly from there.  Also the miles-to-empty reading is always conservative in that it will reach zero but still have some reserve petrol in the tank.  This is to stop people running out of fuel and blaming that the gauge said otherwise, though I have never had the courage to run it right down to zero (had it down to single figures though) and that wouldn't be good if you suck up the crud that lies in the bottom of the tank. 

I had a Mercedes Benz E-Class (W211) before the Focus I'm driving now and the gauge was pretty accurate so this is something new to me. 

The mk3 Focus gauge is really inaccurate, much worse than the mk2 gauge ever was!!  I've run both down to 0 miles on the range...still a long way off getting the full 53 litres in.  The fuel light on the mk3 also comes on far too early, between 70 and 90 miles on the diesel, so you put up with the light for so long that you don't notice when you're actually running out.   So yeah, basically it's just another 'quirk' of the mk3 that you have to put up with, nothing you can do about it.