Culture.

Now that’s a subject that most leaders would be wise to pay more attention to.

One boss who does: Ginny Rometty at IBM .

And to her benefit. Currently in charge of sales and marketing and strategy at Big Blue–and No. 8 on Fortune’s Most Powerful Women list–Rometty is mentioned in Fortune‘s current cover story about IBM as a possible successor to CEO Sam Palmisano.

Recently Rometty spoke about culture at the Yale CEO Summit. Her talk to be so good that it’s worth my sharing a few of her points here.

Culture, Rometty told the audience, has become the defining issue that will distinguish the most successful businesses from the rest of the pack.

For instance, Ford got back on track by rerouting its culture. CEO Alan Mulally rallied faithful followers. And in turn, the entire organization refocused on Ford’s core value: quality.

The biggest cultural challenge for corporate leaders: social media. Rometty cited Nielsen research that shows social media accounts for almost a quarter of the time Americans spend online. Social media’s consumption of time spent on mobile devices? Around 50%.

So, she said, “Your message has to be a dialogue, and it has to be authentic.” Especially, she added, since some research suggests that consumers trust information from each other twelve times more than they trust messages or ads from companies.

Most importantly, “You have to rethink the way you treat and talk to employees,” she added.

On Facebook, Rometty said, more people “self-identify” with IBM than with any other organization. Given this reality, IBM decided to cede control to its employees–that is, let them devise behavior guidelines.

This process began in 2005, when IBM employees used a wiki to create a set of guidelines for all IBMers who wanted to blog. Since then, IBMers have evolved the guidelines to include all social media.

Today, IBM’s “Social Computing Guidelines” aren’t necessarily what would come out of an Office of the President. For example, No. 10 of 12 on the list is: “Don’t pick fights, be the first to correct your mistakes.”

Hey, it works. This sort of culture-carrying throughout the organization has helped propel IBM near the top of
Fortune
‘s Most Admired Companies list. And it has helped propel Rometty’s career as well.

Now that she’s close to the top, she believes more than ever: “Culture has to come from the bottom up.”