New York Times columnist Nick Kristof once said that if Lehman Brothers had been Lehman Brothers & Sisters, the world might not have ended up in the soup it’s in.

That’s a good line. And champions of gender diversity flog it far and wide now that the topic of women and power is hotter than ever. That’s because, as Kristof notes in today’s op-ed, “Don’t Write Men Off Just Yet,” women became the majority of the U.S. workforce this year. This is a first. Moreover, colleges and graduate schools handed out many more diplomas to women than to men this spring. And the new economy — or should we call it “the new new economy”? — tilts toward talents such as communication and collaboration, which many say are quintessentially female skills.

Even if you don’t believe the latter point, you must agree that women are better positioned than ever. Yet they (or I should say, we) are not assuming power as you would expect. At the Aspen Ideas Festival two weeks ago, I moderated a panel called “Women Can Lead. Will We Let Them?” and mentioned these facts: Only 13 Fortune 500 companies have female CEOS. Five states have female governors. Congress has 17 women in the Senate and 76 women in the 435-member House of Representatives. Speaker Nancy Pelosi is the boss of the house, but those stats are generally pathetic.

What gives? One of my panelists in Aspen was Rockefeller Foundation CEO Judith Rodin, who surmised: “Women fall out of the pipeline at a faster rate than men do.” One reason — perhaps more significant than the struggle for work-family balance, Rodin says: “Women think about power negatively. I was called aggressive and ambitious because I enjoy power. That was a negative.”

Trained as a research psychologist, Rodin has studied gender issues for many years — and has long embraced her inner leader. She is the first woman to run the Rockefeller Foundation. Before that, she was the first female Ivy League President–at the University of Pennsylvania, where drew attention as the highest-paid University president in the U.S. Never shy about showing her clout, she’s now on the boards of Citigroup (C), Comcast (CMCSA) and American Airlines (AMR).

Most women, Rodin contend, discount their value. “Women have negative illusion,” she says, noting that we believe we’re not up to a task when a guy, possessing a sliver of the competence that we have, readily take it on, no problem.

I think Rodin is right. I’m on my way back to Aspen for the start of Fortune Brainstorm Tech and will explore the topic at a Friday Most Powerful Women lunch. I’ll be interviewing Juniper Networks (JNPR) CEO Kevin Johnson, who happens to have more women in top-level jobs than most other Silicon Valley companies. Let me know: What should I ask Johnson? And what do you think it takes to get more women in CEO posts, especially in Silicon Valley?