Given the FBI investigation and the indictments of many shrinks who handed out MPD diagnoses... Given the absolutely absurd claims of Satanic torture made by many of the victims...
Given the way the brain *works*...
I simply cannot believe that people contain
multiple personalities.
Now, DID may be somewhat different, as the name suggests. While I do not think that you could have two separate 'people' living in your brain, with separate memories, abilities, personalities, etc., who have no knowledge of each other, (the structure of the brain simply defies this,) I do think that it is possible that, under conditions of high stress, certain aspects of your brain might turn 'off' or 'on'.
To draw a benign example, let's say you smell strawberries, and suddenly remember picking strawberries as a child. Up until you smelled the berries, you had no recollection of picking berries as a child, but the scent awakened the memory.
Let's say that you are normally an outgoing, friendly person, but under stress, you become withdrawn and hostile. While under stress, you act differently than you would normally.
Later, when you are not under stress, you act the way you normally would. You might even actively try not to think about the things which happened while you were under stress.
Still later, things get stressful again, and your memories of the past resurface and come flooding back.
It's not that you have different personalities, but that your one personality has different coping strategies for different situations--thus, disassociation.