New York: The charisma king of the 2008 presidential field. The world's best golfer. The captain of the New York Yankees. Besides superstardom, Barack Obama, Tiger Woods and Derek Jeter have another common bond: Each is the child of an interracial marriage.

For most of US history, in most communities, such unions were taboo.

It was only 40 years ago - on June 12, 1967 - that the US Supreme Court knocked down a Virginia statute barring whites from marrying non-whites. The decision also overturned similar bans in 15 other states.

Since that landmark Loving-versus-Virginia ruling, the number of interracial marriages has soared; for example, black-white marriages increased from 65,000 in 1970 to 422,000 in 2005, according to Census Bureau figures.

Factoring in all racial combinations, Stanford University sociologist Michael Rosenfeld calculates that more than 7 per cent of America's 59 million married couples in 2005 were interracial, compared to less than 2 per cent in 1970.

More diversity

Coupled with a steady flow of immigrants from all parts of the world, the surge of interracial marriages and multiracial children is producing a 21st century America more diverse than ever, with the potential to become less stratified by race.

"The racial divide in the US is a fundamental divide... but when you have the 'other' in your own family, it's hard to think of them as 'other' anymore.

"We see a blurring of the old lines, and that has to be a good thing, because the lines were artificial in the first place."

The boundaries were still distinct in 1967, a year when the Sidney Poitier film Guess Who's Coming to Dinner - a comedy built around parents' acceptance of an interracial couple - was considered groundbreaking.

The Supreme Court ruled that Virginia could not criminalise the marriage that Richard Loving, a white, and his black wife, Mildred, entered into nine years earlier in Washington, D.C.

But what once seemed so radical to many Americans is now commonplace.

Many prominent blacks - including Supreme Court Justice Clarence Thomas, civil rights leader Julian Bond and former US Senator Carol Moseley Braun - have married whites.

Well-known whites who have married blacks include former Defence Secretary William Cohen and actor Robert DeNiro.

Last year, the Salvation Army installed Israel Gaither as the first black leader of its US operations. He and his wife, Eva, who is white, wed in 1967 - the first interracial marriage between Salvation Army officers in the United States.

Opinion polls show overwhelming popular support, especially among younger people, for interracial marriage. But interviews with interracial couples reveal varied challenges.

Bob Jones University in South Carolina only dropped its ban on interracial dating in 2000; a year later 40 per cent of voters objected when Alabama became the last state to remove a no-longer-enforceable ban on interracial marriages from its constitution.

Taunts and threats, including cross burnings, still occur sporadically. In Cleveland, two white men were sentenced to prison earlier this year for harassment of an interracial couple that included spreading liquid mercury around their house.

More often, though, the difficulties are more nuanced, such as those faced by Kim and Al Stamps during 13 years as an interracial couple in Jackson, Mississippi.

Kim, a white woman raised on Cape Cod, met Al, who is black, in 1993 after she came to Jackson's Tougaloo College to study history.

Together, they run Cool Al's - a popular hamburger restaurant - while raising a 12-year-old son and 10-year-old daughter in the state with the nation's lowest percentage (0.7) of multiracial residents.

The children are homeschooled, Kim said, because Jackson's schools are largely divided along racial lines and might not be comfortable for biracial children.

She said their family triggered a wave of "white flight" when they moved into a mostly white neighbourhood four years ago - "People were saying to my kids, 'What are you doing here?' "