Even as Martha Stewart's new co-CEOs, Wenda Millard and Robin Marino, announced solid quarterly profits this morning, they have a raft of challenges ahead--a cloudy ad outlook, a sputtering merchandising deal with Kmart, and the inevitable ego-balancing that is part and parcel of any partnership at the top. Co-CEO set-ups such as this one at Martha Stewart Living Omnimedia (MSO) are so unusual that, among Fortune 500 companies over the past 10 years, only 15 such arrangements have existed. Analysts expressed skepticism about the power-sharing reorg last month after former CEO Susan Lyne departed suddenly. With the stock down 42% in the past 12 months, concerns linger, particularly as iron-willed Martha looms powerfully in the background.

On today's conference call with investors, Charles Koppelman, MSLO's chairman, said of the new duo at the top: "One plus one equals three." But when Koppelman phoned me last month to talk about the set-up, he struggled to justify why this is an ideal arrangement for the company. Bob Daly and Terry Semel, the onetime co-heads of Warner Brothers, were a dream team, he noted. Indeed, Daly and Semel (who went on to lead Yahoo (YHOO) ) once ruled Hollywood, but they weren't managing a publicly traded company, which is more challenging. Remember the doomed partnership of Sandy Weill and John Reed at Citigroup (C)? About that, Koppelman quipped, "Citigroup didn't work because those two guys had one agenda—to get the other guy out!"

The logic at MSLO is that Millard and Marino, both 54, have clearly designated charges. Millard, who rose through the magazine industry before heading sales at Yahoo, oversees Martha's magazines, television business, and Internet operations. Marino, who was president of Kate Spade and worked for a power couple (Kate and Andy) before joining MSLO three years ago, heads the vast merchandising businesses, which includes an ever-expanding list of retail partners such as Wal-Mart (WMT), Costco (COST) and Macy's (M).

Meanwhile, Stewart, who is prohibited from serving as a corporate officer or director for five years by her 2006 SEC settlement, is solidifying her grip. She's a member of her company's new office of the chairman. When I asked Koppelman whether she's more involved than ever, he laughed and said, "What a question!" Stewart holds 53% of her company's stock, 91% of the votes, and ever-increasing sway.

To many Martha watchers, this seems like a lot of cooks in the kitchen. Says Koppelman in response:  "I'll bet you that in three years, you'll say 'Wow! What a genius move!'" The wager? Dinner in 2011. Winner chooses the restaurant.

P.S. Robert Huang and Kevin Murai are co-CEOs of Synnex, a growing business processes company on the Fortune 500. Do you know any other co-CEOs who have successfully run a major company? What's their secret?