I think the choice of "boy or girl" is an interesting topic and one discussed among expecting parents and their family and friends all the time. Expecting parents are often heard saying "It doesn't matter, boy or girl, as long as he or she is healthy". I said it, but it wasn't really how I felt.
When I was pregnant with my first child and I desperately wanted a little girl. While I knew that I wanted more than one child, and I wanted at least one of each sex (and secretly dreamed of twins, one of each) I knew that with a single birth, I wanted a girl first. My reasons have nothing to do with being a girly girl and wanting to pass that along, I wanted a girl first to avoid my daughter going through what I did with my older brother and all his possessive and protective tendencies. He hung up on boys that would call, slammed the door in their face if they came over, and convinced our dad that these boys, for whatever reason, were not the type of guys I should be associated with. He really made it quite hard to get a date. I managed though.
I not only had my precious baby boy first, but followed with my darling daughter and the age difference (33 months) is exactly the same as between my brother and I. She'll have me on her side so it will all work out.
When it comes to the matter of boys or girls, I've heard some pretty interesting reasoning as to why one parent (or both) have a specific reason for wanting one or the other. My husband was thrilled to find out we were having a boy and freaked out when we found out baby number two was a girl. He went into instant protection mode and I'm not sure he'll ever recover, she's 2.
I have one friend who will deliver in December and while she has 2 girls already, she wants a third. She is afraid she will not know how to relate to a little boy. She was raised with sisters, most of her family is female, and she feels she has not had enough exposure to boys to know what to do with one. She is going to find out how wonderful raising a boy can be and she will do just fine. Her husband is ecstatic!
I have another pregnant friend, who is pregnant with her second child, the first being a girl, and I was surprised to hear that her husband was hoping for another girl. He believes that all little boys are "thugs" and doesn't want any part of them. Which seems pretty funny to me, because what happens when his girls are ready to date? Poor Dad.
In the case of parents who are unable to conceive (or those that choose not to) and go the adoption route, they are always asked boy or girl, and they get to actually choose. Some of these choices are made out of a preference of one sex to the other, but I think in a lot of cases the parents just want whichever they can get first, and again you'll hear these expecting parents say, "It doesn't matter, boy or girl, as long as he or she is healthy."