At this week’s Fortune Most Powerful Women Summit in Laguna Niguel, Calif., former Xerox CEO and Chairman Anne Mulcahy sounded a warning to her fellow powerful women. After decades of taking pride in being trailblazers and pioneers as the first female board members at companies, women should now find taking such jobs as the first woman unwise, Mulcahy cautioned. “It's a bad sign,” she told the audience, according to reporter Colleen Leahey. “Boards without women – blacklist those suckers. It's 2011. They've had the time – it's significant that they don't have women.”

I’ll resist invoking the Virginia Slims slogan for everyone’s sake. But it is dramatic how far we’ve come—from a time when being the first female director of a board was a common experience to a day when one of the most respected women in business suggests that female leaders have enough choices to say no; that in 2011, boards without female members are so behind the times that they should come with warning signs.

All of which raises an interesting question. If given the opportunity to join an all-male board, should women really “blacklist those suckers,” as Mulcahy reportedly said? Are the challenges they’d face in being a member of that board so great as to outweigh the potential good they could do by joining? Or can women have more impact by joining a board where there is already some semblance of diversity?

At least among the largest company boards, the number of women who will have to make that call is dwindling. As of March 2011, there were just 23 global companies that did not have a female director, according to an article in the Atlantic that used data from GovernanceMetrics International. (At least one of those companies, IAC, is no longer on the list: In September, it added Chelsea Clinton and venture capitalist Sonali De Rycker to its board.) Across the entire S&P 500, only 10 percent of companies don’t have women on their boards, according to an October 2010 study from the executive search firm Spencer Stuart. That’s down from 14 percent in 2000, the same study reports.

At the same time, female representation on boards is still a major issue. The percentage of female directors, which hovers around 20 percent, has been at a standstill over the past decade—Spencer Stuart finds that there has been no increase in that ratio since 2000. The research firm Catalyst reports an even lower number, 16 percent, putting the United States behind Finland, Sweden and Norway, which actually has a law requiring 40 percent of all board members at Norwegian companies to be women. Those low percentages persist despite the fact that study after study has shown that more diverse boards are associated with greater company performance.

I get what Mulcahy is saying. Why should women in positions of power join a club, as she puts it, that they may not want to be a part of? At that level, most women have multiple commitments, and joining a board where they’re treated like tokens rather than assets may not be the best use of their time. In addition, they may be able to have more of an impact on a board that is already forward thinking and receptive to diversity.

Still, I have to think that even Mulcahy would agree those boards need women, and that even boards with women need more than they already have. It’s great that there’s been enough progress that female leaders now have so many options. But the only way to make sure it continues is for some women to take on those less desirable roles and carve out pathways for the rest. Even if it means working with the suckers.

Jena McGregor writes The Washington Post’s Post Leadership blog.

Disclaimer: Anne Mulcahy is on the board of directors for The Washington Post Company.

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