I have 900 miles on mine right now. I have about 450 miles (2 weeks worth) on this tank. For this tank, I am averaging 18.6 with most of it rural driving at about 60mph coupled with some town driving. You really have to take everyones experiences with a grain of salt, because the conditions vary widely. You have to expect significant differences when comparing driving in hilly terrain with a lot of stop and go, or much big city driving to driving on flat ground with little stopping.
I can tell you that under the same conditions my old 2000 F150 with a 5.4 and a 3.73 rear end got 15.5-16MPG. The new 5.0 is MUCH more powerful than the old 5.4 and a fair bit more powerful than my current 2010 Chevy work truck with the 5.3. BTW all vehicles were/are 4x4's
When my truck is fully warmed up with the cruise set on about 58 and driving on flat ground, I get about 24 mpg.........but that is not real world, day to day mileage. It is purely optimum conditions.
I don't know what to expect after about 10K miles, but I would guess about a 1mpg increase.