As a recently-out transvestite (horrible term, cross-dresser isn't much better. I'm working on androgynous), I think there's far too much emphasis on the 'rules' and labeling every permutation of the transgender spectrum. A lot of people don't necessarily want or feel the need for society to try and fit individuals into the 'normal' male/female paradigm and want to have the right to be as masculine or feminine as they like without it undermining how they are considered as a person.
One theory (which I subscribe to) is that there are 3 main facets of gender/sexuality.
Sexual Identity - This is the physical body that you are in and how you feel about it. For the majority of people it's relatively straightforward but it can be more complex for people who for whatever reason have a mix of male & female biological traits or those who wish to change their physical sex.
Gender Identity - This is in the mind, so to speak, and possibly the most overlooked and misunderstood area. This is not necessarily a case of 'I feel like a boy' or 'I feel like a girl', it is a scale. Plenty of people might consider may wish to express themselves as masculine or feminine as they like in any given moment, but feel completely happy in their body.
Sexual Orientation - So we know what this is, right? It is also a scale. So you're a 'straight' guy but you can't help but think that this one guy is cute? Does this make you gay? Bisexual? Bi curious? My response is - why the fuck does it matter? I've known a few guys who for intents and purposes were straight guys, but with the right mix of flirty fun and confidence, can find another guy attractive. Lets face it, we don't fancy people simply on the basis that they are of the gender that we've 'decided' we like.
Sorry for the wall of text, and apologies if this duplicates previous points, I read pages 1 & 2 then skipped to 5. Although I feel the discussion's gone off topic...