I can't say I know all too much about sex changes, having never been exposed to anybody who has had one, other than a couple of people I've seen on television which is just... not worth even talking about. But the motives behind having one have already been described. I think wanting to have one, and actually getting one have an effect on one's actions. Unfortunately I can't speak on someone's behalf and will leave that there, it's not very clear and I'm sorry; I just know too little.
The other issue raised here was gays. I myself am gay but live nothing to the stereotype that gays are most grouped into, that they are "pansies" and what not. Having been told I'd be the least expected in my group of friends to be gay is something that may strike people as odd because they have predetermined views of what a gay person should be.
When introduced to someone by my friends, they sometimes mention that I'm gay. What this does to the person that meets me is treat me forever differently because I'm part of a minority that society has instructed people to think of me (strangely more so with girls because the chances of having a relationship with me then become zilch). It's not that I've changed the way I act, I'm exactly the same person I was before, but the people around me change the way they act because I'm now considered a different person. This doesn't very often lead to a friendship of any sort.
On the other side of the coin, if I'm to tell someone that I'm gay into a well-established friendship, there's no difference in their perception of me, because they've gotten to know the person I am. It might even change their views, it has in one case one of my close friends was originally quite homophobic but when I told him about me, nothing changed. I actually find that quite amusing, how discursive people can be.
One final topic I wanted to bring up which hasn't been mentioned directly is heterosexuality. Paraphrased as being "Everything about a gay man except sexual orientation," is this not calling upon societal stereotypes to identify someone who seems like a gay person? I can't quite remember the point I was going to make with this, but there's no reason it can't be discussed...