Depends on who mapped it.
my mate had a revo (i think) map put on his old car, he unplugged the battery and when he connected it up it had lost all power, he rang up the company who maped it and they said cause hes unplugged his battery he has lost some 'settings' etc and that its just reverted to a basic revo (ro what ever company it was) map. they then re-did the settings as a "good will" gesture, but told him if he lost the 'settings' again he will have to pay for them to be put on.
never heard anyone else having this problem, but it certainly wasnt running as fast as it previously was...