Regina Herzlinger, of the Manhattan Institute, puts it in perspective:

In 1988, worried about the decline in female MBA applicants, I had publicly contended that the CEO barrier for women — the glass ceiling — was a myth perpetrated by the "I am victim, hear me whine" branch of the women's movement...But I stuck to my guns: The paucity of female CEOs was primarily caused by the paucity of qualified candidates, not by prejudice.

So, Herzlinger assumed that these days a reunion of Harvard Business School grads from 1964-1979 would include many more CEOs, who had spent their years climbing the ladder. She was right:

I found that by 2004, 16 women led Fortune 1,000 companies and many more headed large private firms and great universities and other non-profits. This admirable, accomplished and diverse lot included Meg Whitman of eBay and Andrea Jung of Avon.

But there was a bigger shift at work:

I assumed that female managers wanted to shatter the glass ceiling; but, as it turned out, many wanted something else entirely. As women, blessed with creativity and the flexibility to re-create themselves more freely than men, many rejected big corporate careers, opting to become entrepreneurs.