We can do it only on the most limited of basis for the moment -- about the best I've seen is a hair prop by Lourdes (still in beat, sorry) that allows you to move sections of it, but not individual strands. The reason for that is pretty obvious: computing power. I don't know the specifics of how they did it in FF, but in Monsters Inc, they created what were called Master Hairs, that were used to direct the motion of all of them - you would have something like 1000 strands assigned to a single Master Hair, and they would all move more or less in concert. But that takes a whopping amount of power when you consider that the good doctor in FF had 75,000 strands and the blue monster had 225,000.