Thanks to Jeff for showing me this:
http://www.amsa.org/amsa/homepage/takeaction/amsaoncall/11-05-09/Controversy_on_Valentine_s_Day.aspx I had heard that almost 50% of doctors are now women, but I didn't realize even within being doctors there was a division of labor (i.e. few women go into surgery, the more well-paying positions). Also there's that ~$17,000 pay gap among newly trained male and female doctors--to put things in perspective, that pay gap is pretty close to my current annual salary (yes, being a grad student is not something one does for the money, haha!)
Anyway, this phenomenon is certainly not limited to the medical professions. Rather this is a phenomenon that occurs in almost every type of career--the jobs "at the top" which are the most prestigious and well-paying are dominated by men. First of all, there is a division between what men and women major in during undergrad--currently women are the most underrepresented in computer science and engineering, which happen to lead to the most well-paying jobs in the country, and women are way over-represented in psychology/counseling, which leads to some of the worst paying jobs (in social work). But even in disciplines which are now 50/50, like biology/medicine and law, there will still be a concentration of men in the top positions while women are found concentrated in the part-time/temp jobs at the bottom.
This brings to my mind a great book I recommend for anyone who is considering becoming a parent, "Mothers on the Fast Track: How a New Generation can balance family and careers" by Mary Ann Mason and Eve Mason Ekman (a mother-daughter team that wrote the book together, aww). Mary Ann Mason is awesome, I saw her when she came last year to the sociology department at UCSD and also at a math conference in San Francisco--I was impressed both times by how articulate and eloquent she was! She was the graduate dean at UC Berkeley and has worked very hard to improve the UC system's benefits for graduate student parents. Anyway, the book is a systematic study on how societal expectations surrounding family obligations can help explain why, even though more and more women are entering graduate and professional schools, the numbers of women in the top levels of almost every profession have remained stagnant.
What this book doesn't address (I think there's maybe one sentence about it) is that in many fields there is still a strong element of sexism and discrimination which is holding women back in addition to the other forces holding women back in every field. I already knew this was true in mathematics, but I didn't realize this was true even in fields where the numbers of men and women are equal, like in the medical sciences. This just goes to show that the goal of feminism is not merely a numbers game--the goal is not that men and women make up 50% of every profession. The goal is that someday women will be welcome to pursue whatever career/job they want to at even the highest levels, while being able to enjoy the same quality of life that men in those positions do. We still have a long way to go.