It sounds innocent enough, but then watch the movie Gattaca (sp?) and see what it could evolve into... completely genetically engineered people that become a higher class than naturally born ones. Creepy!
My neighbor has four sons and aches for a daughter. They are college and highschool age so this is probably too late for her. She says that my mother is so lucky to have three daughters. I would consider doing it if I found myself in her situation, or if my hypothetical husband and I were carrying a gender linked genetic disease.