Catalyst released its annual census of the Fortune 500 today http://www.catalyst.org/press-release/161/2009-catalyst-census-of-the-fortune-500-reveals-women-missing-from-critical-business-leadership. It's grim reading. Women are making NO progress in the boardroom and the executive suite. Women make up 13.5 percent of executive officer positions (defined as people appointed or elected by the Board of Directors, including the CEO and two levels below). At the board level, women are doing slightly better, occupying 15.2 percent of seats. Most companies (90%) have a token woman on their board, but only one in five companies have at least three female board members. At this rate, we'll have to wait 70 years before we see parity in the boardroom.
What's going on? Don't these companies know that putting more women in senior management means better decisions, higher profits, stronger share price, more prudent risk taking and a more well-rounded, thoughtful and effective management team?
Apparently not. It's the mirror theory at work again. Most board seats (and senior executive positions) are filled with Caucasian men who tend to like to work with people who look like them, act like them and profess the same values that they do. Subtle biases and stereotypes are at work here. Many studies have demonstrated these biases, but one study in particular found that female leaders had to be perceived as both strong and sensitive to be considered effective. Male leaders only had to be perceived as strong. 
Now before I get a bunch of e-mails about how "the worst boss I ever had was a woman," let's look at the token issue. When a woman makes it to a leadership position, she is usually a "token" (i.e. a numerical minority representing 15 percent or less of the total number in a group). Tokens are constantly thrust into stereotypical roles, are on display, feel more pressure to conform and make fewer mistakes. They try to be socially invisible and not stand out, and find it harder to gain credibility. Tokens are also more isolated, excluded from peer networks, have fewer opportunities to be sponsored and face misperceptions of their identity. At the same time, those members of the dominant group tend to erect and maintain boundaries that exaggerate group differences and strengthen the common bonds between members of the majority group. The token's resulting isolation and 'differentness' leads her to be excluded from informal gatherings and further perpetuates the maintenance of the token as a minority group. In addition, because the token usually wants to fit into the dominant, and usually high status group in some fashion, she often distances herself from other minority members in an attempt to further differentiate herself from the minority group. This suggests that high-level women managers often do not actively promote or encourage other women fearing competition from them. So the fact that you're a highly capable manager and leader, might become obscured by all the other organizational nonsense you have to deal with in order to just get your job done.
How do we fix this problem? There are a number of solutions. Here's a very brief list of some of them:
 "The Strong, Sensitive Type: Effects of Gender Stereotypes and Leadership Prototypes on the Evaluation of Male and Female Leaders." S.K. Johnson, S.E. Murphy, S. Zewdie and R.J. Reichard. Organizational Behavior and Human Decision Processes, Vol. 106, Issue 1, May 2008, pp. 39-60.