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.
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.