We have the 3.5L Ecoboost in an FX4 SuperCrew with the Max Tow package, Off Road package and 6.5' bed. It's been pretty impressive in the two weeks that we've owned it.
The F150 replaced a 2004 Nissan Titan Crew Cab (5.6L V8, 5.5' bed, trailer tow package). We have an X19H, and even though you are not supposed to tow for the first 1000 miles, the camper has been behind the new truck twice. It feels like the Ford tows better than the Nissan did. That 3.5L has good low end torque and seems to perform pretty much according to the specs. This vehicle is also my daily driver, so I wanted a pickup that got decent mileage in town. We seem to get between 12 and 15mpg (in Colorado) while towing and 17 to 21 with a mix of freeway and side street driving. I expect mpg to stabilize a bit in the next couple of thousand miles. This is probably as much about driving habits as anything else; it is fun to hear those turbo chargers sing.
As far as longevity goes I did a bit of research before pulling the trigger on the Ford. Turbo technology has improved quite a bit over the years, and Ford seems to be putting a lot of research and effort into this line of engines. I did not purchase an extended warranty/service plan, but I will keep tabs on how these engines perform to determine if that might be good risk coverage down the road.
It turns out that the Nissan engines had problems with cracked exhaust manifolds, and our Titan was no exception. That was an expensive and time consuming fix, so I guess it is all relative.
If you have not driven the 3.5, you should. I was surprised. Also, if you are interested in some of Ford's tests, check out the Torture Test
(realize that it was Ford that performed the tests and prepared the videos).
Hope this helps.