The American Institute of Physics just released a study of gender ratios in faculty, undergrads, etc., in physics and astronomy. Amazingly, they apparently found no "leaky pipeline" at the faculty level - in other words, the same percentage of women become faculty as the percentage of men - after accounting for the ages of faculty and how many people of each gender received degrees "back then."
The researchers do point out however, that this does not mean that all is rosy: they may not have gotten there easily, and we know nothing about whether the climate they work in is good. For example, from 1999-2003, only 18 schools awarded at least 40% of their bachelor's degrees in astronomy to women (my Alma Mater included). And that 40% of women physicists who had children felt that their careers progressed more slowly than their male peers, as opposed to only 25% of women physicists without children.