In the latest Atlantic, Hanna Rosin has a very interesting article/manifesto that rails against the "cult of breast-feeding":
The medical literature [on breast-feeding] shows that breast-feeding is probably, maybe, a little better; but it is far from the stampede of evidence that Sears describes. More like tiny, unsure baby steps: two forward, two back, with much meandering and bumping into walls. A couple of studies will show fewer allergies, and then the next one will turn up no difference. Same with mother-infant bonding, IQ, leukemia, cholesterol, diabetes. Even where consensus is mounting, the meta studies--reviews of existing studies--consistently complain about biases, missing evidence, and other major flaws in study design. "The studies do not demonstrate a universal phenomenon, in which one method is superior to another in all instances," concluded one of the first, and still one of the broadest, meta studies, in a 1984 issue of Pediatrics, "and they do not support making a mother feel that she is doing psychological harm to her child if she is unable or unwilling to breastfeed." Twenty-five years later, the picture hasn't changed all that much. So how is it that every mother I know has become a breast-feeding fascist?
It's not that numerous studies haven't found a small but consistent correlation between breast-feeding and other variables, such as reduced incidences of gastrointestinal infection and increased IQ scores. (Although it's also worth pointing out that the IQ link remains questionable.) However, as Rosin notes, these relatively minor correlations are often considered in a vacuum, and not weighed against the burden of breast-feeding.
Breast-feeding is a serious time commitment that pretty much guarantees that you will not work in any meaningful way. Let's say a baby feeds seven times a day and then a couple more times at night. That's nine times for about a half hour each, which adds up to more than half of a working day, every day, for at least six months. This is why, when people say that breast-feeding is "free," I want to hit them with a two-by-four. It's only free if a woman's time is worth nothing.
The larger point is that the happiness of the mother is far, far more important in shaping the life of the child than whether or not the child was breast-fed as a baby. (See, for instance, this interesting study on the long-term consequences of "unwanted childbearing".) If breast-feeding is an undue burden, or if breast-feeding creates tension between the mother and father, then it might be time to buy some formula.