They take vows of devotion for richer or for poorer, but in Hollywood, when the wife's star eclipses her husband's, it can often spell disaster for the marriage.

Just look at Hilary Swank, 31, the two-time Academy Award-winner who infamously forgot to thank her husband, Chad Lowe, 38, when she gave her first best actress Oscar acceptance speech in 2000. The pair announced their separation in January, and on May 26, People magazine's Web site reported that she will file for divorce.

"Hilary Swank and Chad Lowe have jointly decided to divorce," Jeffrey A. Bernstein, an attorney for the couple, told the magazine. "They continue to be friends and have the utmost respect for one another."

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Meanwhile, Madonna's marriage to director Guy Ritchie is said to be in a rough patch; many blame Jessica Simpson's split from former boy-band husband Nick Lachey on her rising star; and Reese Witherspoon and less famous actor-husband Ryan Phillippe are in and out of the splitsville rumor mill.

Bruised egos, better screen billing and bigger paychecks are just some of the things that can destroy celebrity power couplings, says James Robert Parish, author of the forthcoming "The Hollywood Book of Breakups."

"We go over the decades and things haven't changed much." Parish said. "We do have these very powerful women who are more famous. Their husbands are in the shadows, and no matter what they do — even if they're the most obliging, considerate and faithful husbands — the press is always out to stir up something to get good copy. And very often it's a self-fulfilling prophecy."

Lasting marriages are hard enough to maintain, but when the wife's name carries with it a seven-figure salary and the scrutiny of the American public, it can be downright impossible to keep up expectations.

"When the husband is carrying up her skirts in the background, it creates this perception that he's just a hanger-on, he's a mooch or it can't last because his ego and his psyche can't deal with it, which may or may not be the true case," said Parish, who cited only one real power couple that has lasted through recent Hollywood history: Paul Newman and Joanne Woodward.

Strong female personalities have had trouble succeeding at marriage since Tinseltown first started churning out movies. Mary Pickford, Bette Davis and Joan Crawford are among the divas whose egos have overshadowed their husbands, leading them to divorce more often than they won Oscars.

"You see the same things in marriages where they're from two different show business mediums," Parish said, citing, for example, singer Marc Anthony and Hollywood heavyweight Jennifer Lopez. "Now he's certainly famous in his own right, but being married to her it's always Jennifer Lopez and Marc Anthony, and it's not being just politeness, it's because it's the perception of who is the more powerful, wealthier, influential person."

While Anthony and Lopez seem happy so far, her previous marriage, to backup dancer Cris Judd, ended after only 16 months. Her first marriage, to waiter Ojani Noa, lasted less than a year.

Another female superstar who married a not-so-famous backup dancer — need we name her? Britney Spears — is also said to be having trouble with her husband, Kevin Federline.

Luckily for these ladies, divorce doesn't carry with it the same stigma it did when Pickford shockingly divorced her husband to marry Douglas Fairbanks Sr.

According to the National Marriage Project at Rutgers University, the U.S. divorce rate is almost twice that of 1960, with the average American carrying a 40 to 50 percent chance of divorce in his or her lifetime.

Nationally, those chances decline by 30 percent when the annual income of a couple is more than $50,000, by 24 percent if a baby is born seven months after the wedding and by 24 percent if the couple marries after age 25 without having a baby first.

The National Marriage Project's 2005 "State of Our Unions" report did find that women are more likely than their male counterparts to stay divorced, as men tend to remarry more often than women.

The chance of divorce does rise as the woman's salary approaches or surpasses that of her husband, said David Popenoe, the co-director of the National Marriage Project.

"It may have something to do with the fact that the women who make a lot of money are able to divorce and they're able to be independent," he said. "They don't have to depend on their husband financially, so it makes it easier to divorce."

Still, the added pressure of stardom is another barrier to a healthy marriage.

Hollywood's newly crowned Oscar-winner and highest paid woman, Reese Witherspoon, has been rumored for years to be in a rocky marriage with less-famous actor Ryan Phillippe.

But the actress, who has two children with Phillippe and has publicly spoken about going to couples therapy with him, places her focus on the home.

"Marriage and family come before everything," Witherspoon told US Weekly in 2004. "You don't want to make a movie at the cost of your relationship."

Only time will tell if these two will make it last. But for unmarried stars, the best advice seems to be steer clear of dating a peer.

"It usually works much better when one of the mates is in the industry and the other one is, as they used to say in the trade papers, a non-pro — not in the industry," Parish said.