To be completely honest, I would absolutely LOVE to have boy/girl twins. Before having children I just visioned having a little boy, then having my little girl, thought after that that I would be done because I would have one of each, but now I have a very strong feeling that b/g twins are in my future sometime and I would be absolutely elated. It would give my son a brother, and my daughter a sister. Each time I had a feeling about gender I was right on. I bought boy stuff before getting pregnant with a boy, bought girl stuff before getting pregnant with a girl, now I feel compelled to buy both boy and girl stuff because something tells me that I will need both. I don't know perhaps that is weird, but that is just what I have noticed.
If I only had a singleton I wouldn't have a personal preference as long as baby was healthy. I do know I would feel like I needed to have another to try to balance out the genders if I had a singleton for #3.