That's interesting. A lot of the Culture novels by Iain M. Banks have the premise that anyone can change their sex just by thinking about it, and a lot of characters do, usually more than once (man to woman then back to man again). There doesn't seem, from the books I've read, to be any sense of gender identity whatsoever.
One novel, 'Excession' the main character changes sex from male to female just to be with the woman he loves. She then changes back to male once the love interest is gone. The interesting thing is that these changes are all-encompassing (ie a man who changes to a woman can then proceed to give birth and has the full genetic makeup of a biological woman). In another novel, a character changes from male to female just to see if being the other gender will make them any more attractive.
There doesn't seem to be any permeating sense of core identity with any of these characters at all. They choose which body fits them for a given purpose, not because of who they are and see themselves to be.
As a result, these novels don't, in my opinion, provide any insight for non-transgendered people, or relevance for transgendered people, other than to provide an entertaining read. I'm not sure it's actually possible for an author who isn't transgendered to accurately portray such characters in a wholely realistic way. The real-world experiences and predjudice faced could be replicated... but unless an author actually knows what it feels like, the emotional aspect and psychological interaction is, I think, something that no amount of research can ever fully compensate for.
