Instapundit links to an article that claims breast sizes are increasing nationwide for Danish women. The article gives credit to increased nutrition, but I wonder if sexual liberation isn't part of the answer, not only for this, but for men's increasing height as well.
A hundred years ago in Europe, most marriages were arranged, or at least set up, by parents. A young woman's chance of reproducing was correlated more to how conscientious her parents were than to her own appearance. Today, mating is largely a matter of sexual competition. Women with larger breasts are more sexually attractive, and therefore may be more likely to reproduce. If so, natural selection will produce a population of women with larger breasts. Similar comments apply to men's height, because tallness for men is a positive trait in sexual competition.