"Trying" for a boy or girl often just leads to more mouths to feed.
Many women I know already have kids, but the ones who have girls want a boy and the ones with little girls crave having a boy. An acquaintance of mine had two boys, but she always wanted a girl -- so she had another baby which turned out to be another boy. She's still determined to get a girl -- and she and her husband are trying again for a girl. In the meantime, they're going broke. They already have three kids, way more than they can afford or than the planet actually needs. This woman, who seems predestined to only pop out boys, would be the perfect candidate for Preimplantation Genetic Diagnosis -- a process that can determine an eggs' sex.
PGD isn't cheap. It can cost upwards of $3,000 plus the usual approximately $15,000 IVF fee. But I think it might be worth it if it would stop women from rolling the gender dice ... and losing.
Have you ever tried to have another child just to get one of a different sex?