Ecoboost isn't like a button or anything you push, it's just the name of that line of engines -
They've got 3 of them now I think - a 1.0 liter turbocharged 3 cylinder (I think this one will eventually wind up in the Fiesta), a 2.0 liter turbocharged 4 cylinder (Available in the Focus S/T), and a 3.5 liter twin-turbo V-6 available in the F-150 and Taurus SHO (and Taurus Police Interceptor).
All of the engines feature Direct-Injection and variable valve timing. Direct Injection allows these gasoline engines to run high boost on 87-octane fuel, as it virtually eliminates the possiblity of pre-ignition (Fuel is added later in the compression stroke). Variable valve timing allows the ECM to adjust valve timing for optimum power or fuel efficiency depending on the circumstances.
They all feature incredible fuel economy - or incredible performance. Not both. It all depends on how hard you push on the "go pedal" - the V-6 Ecoboost can accelerate the F-150 so effortlessly you don't even realize how much fuel you just burned - just touch the pedal and it's GONE. So....that's why you'll never see a 25 MPG entry on my mileage log lol.
I did get 22.8 MPG once, on a 65 MPH stretch with the cruise set, so I guess it is possible...
*edit - My F-150 idles at 550 to 600 RPM, and flutters and shakes and snorts, kicks out some smoke... rattles a bit too
Ecoboosts are weird sounding.