Did anyone actually read the second link Italiangreyhound posted? www.newscientist.com/article/dn19048-bumpology-choosing-the-sex-of-your-child/ It says there HAVE been studies which may link diet and lifestyle with the gender you conceive:
"Recent studies have also hinted that what you eat may influence your chances of conceiving a boy or a girl. One survey of 740 pregnant women found that 56 per cent of women who had a high-energy diet before conception had boys, compared with 46 per cent of women who ate the least. Eating breakfast cereal, in particular, seemed to skew the ratio towards boys."
"Several other papers have since backed up Mathews’s findings. For example, women who gain weight between their first and second pregnancies seem more prone to having boys the second time around"
"The effect is small: 54 per cent of women in jobs classed as low stress, including the arts, cultural and recreational fields, had sons, compared with 47 per cent of women in high-stress jobs such as manufacturing or construction. But if stress hormones are responsible for skewing the sex ratio, says Ruckstuhl, the mechanism is as yet unknown."
But because there are so many other factors at play, they're not reliable enough to depend on: "None of this is much help for parents desperately hoping for a child of a particular sex, however. This is because although some effects can be seen at the population level, the effects are small. We also don’t know how these different factors interact."
So maybe we shouldn't be so quick to say "IT'S ALL BOLLOCKS AND MAKES NO DIFFERENCE" before we've actually examined the evidence? 
Oh, and You do know how sex is decided right? The sperm. The winning little guy is X or Y and boom you have your girl or your boy.
But the egg "chooses" which sperm to let in. (In fact, it "grabs" the sperm, which struggles to get away... I don't know why this makes me laugh so much) discovermagazine.com/1992/jun/theaggressiveegg55