One of the most interesting features of hemisphere dominance and its link to handedness is the way that it can be overriden in emergencies. I know someone who suffered oxygen deprivation for around 15 minutes at birth, due to being transverse in the womb. The deprivation apparently affected the left hemisphere most significantly. This person is left-handed, but is no good at any of the things sinistrals are supposed to excel at. For all intents and purposes, this person is a dextral trapped in a sinistral shell. Apparently, this sort of last second switch is fairly well-documented.