As for that warranty asterisk, the press release says enthusiasts can up the power "while maintaining the Ford-backed limited warranty." However Ford Motor Co. and Ford Racing are separate entities, and, best we can tell, when you reflash the ECU, your Ford warranty gets supplanted by the Ford Racing warranty. Say you bought a 2014 Ford, that means your five-year, 60,000-mile warranty becomes Ford Racing's three-year, 36,000-mile warranty, if we're reading the fine print correctly. If you have an older car and have driven more than 36,000 miles, then your warranty options are kaput, at least as far as a Ford in-house option. If have warranty concerns, you might also want to consider having a dealer perform the reflash, or at least ask about it.
Once you've got past the small print, what about the numbers? At the moment Ford Racing offers tunes for the 2.0-liter EcoBoost in the Focus ST and the 1.6-liter EcoBoost in the Fiesta ST, and we're told there's a 90-pound-foot boost in torque at the crank after you've pressed the right buttons. Anecdotal evidence from a commenter at Road & Track says he went from 252 horsepower at the flywheel to 254 hp at the wheels, and 272 lb-ft at the flywheel to 354 lb-ft at the wheels, but we can't be sure that his adjustments were within Ford Racing specs. Your mileage, naturally, may vary.
What about custom numbers for the 2.3-liter EcoBoost in the 2015 Ford Mustang? They aren't ready yet, but we're told we'll get something by the end of next year.