There is a really fun fictional novel called Put This House in Order by M. Ruff, it's sort of a road trip story featuring two people with DID. The science of the story is a bit iffy (one of the characters has mastered a sort of internal visualization where his personalities can interact), but from the sound of this article he pretty much nailed the what-it's-like factor (particularly w/r/t the broken development chains of the various personalities).