According to a review of the literature on the efficacy of Prozac and other drugs like it, they simply don't work. The one caveat is that they may have some efficacy versus placebo on "severely" depressed patients, however that could be explained by the fact that patients simply figured out that they were on a placebo.
This isn't surprising at all. In the US (where I presume that these are most prescribed), and in most other industrialized countries, they have a board that reviews the efficacy of all new drugs, determines whether or not they are dangerous, etc. Unlike a for-profit regulatory agency, the FDA has no real incentive to make sure that their recommendations are good ones - they are legally obliged to review medicines, and patients and doctors can't really blamed for listening to recommendations that are supposedly of the highest quality. They can take as long as they want to review them, spend as much money as they want, and can making rulings obviously tainted by bias (both political and coming from drug companies) without much call for reform. Somethings tells me, though, that these findings will do little to tame the public's enthusiasm for public regulators like the FDA, and things like this will continue to come out. I'm very interested in studies on the effects of prescribed amphetamines (Adderall, Ritalin, etc.) - drugs which the FDA promises are safe, and which have burgeoned in popularity in recent years, with children in their single digits taking speed on a daily basis.