12k in 9 months. Usually averaging around 18-19mpg on interstate, 20-21 when keeping it 65mph and less and about 16mpg with more city driving (though I am not complaining one bit my old F150 only reached 16mpg once the whole time I had it). I personally think it drives better and gets mpg now then when it was new. Over all I love the truck and only issue to date was needing the Sync computer replaced after it decided to completely stop working.
-2011 FX4 Eco CrewCab Black w/black leather, 3.73 EL, Back up cam/sensors, remote start, tow package, trailer brakes, power rear window, plasti dipped emblems/mirror reflectors, matching front tint, 2 12" JL1 subs, soon to add 2" leveling kit from www.F150Lifts.com
21k since April. 19.1 overall average. No issues whatsoever. Absolutely love the E.B. I have had a 94 96 98 2001 in 150's. Then 03 F250, back to 05 F150 and put 242k miles on it. Traded it for used 07 F250. Drove that a year 45kmi. Traded the 07 for this Ecoboost. Of all the Ford trucks since 94 the EB is the most rounded and satisfying. Comfort and power to match. I told the dealer last week at my oil change the Ecoboost is "economy with an attitude". Lol
I know it isn't me but I have 19k trouble free miles in a little over a year! Love it so far and hoping that there are no major long term problems with these engines. I know a guy that works for VW and he sees a lot of carbon build up problems with their DI stuff so I am very curious.