Just to add, it doesnt take long at all for an ECU to adapt, just a few cycles most of the time. A cycle is a complete suck-squeeze-bang-blow on all four cyclinders (1-3-4-2 I think).
One of the biggest achilles heels on modern engines, that ruins all the fun, is the prevenance of data received from the lambda sensors in the exhaust - emissions are everything these days and reign over pretty much everything else.
A friend of mine is calibration engineer and works on mostly Audi stuff. He's explained to me in the past the difference between the map they start with (basically pure power) and the finished article. By the time they have pulled in the all the emissions to pass-able levels, the difference is huge and and a lot of the time is what the likes of Revo undo with a remap. This compromise is sometimes why you get hollowed out torque curves and flat spots on an apparently perfectly healthy engine - In the battle between power, fuel economy and emissions, something has to give and it's usually power. He's got all sorts of stories from Bosch engineers he knows, apparently the Veyron is capable of a hell of a lot more without any serious strain on the engine!
