"For First Time, Unmarried Households Reign in U.S." reports a current story in Yahoo! News by Maxim Kniazkov. The article notes, correctly, that in the Census Bureau's 2005 American Community Survey 50.2% of American households do not include a married couple, while 49.8% do.
Does this mean marriage is now the minority "lifestyle?" No, not really. When we do an apples-to-apples comparison, the survey shows that of family households (which have, or had, kids), 74% are married.
Some of the bare majority of unmarried households is made of single parents. Kniazkov rightly notes that most of the unmarried households, though, are what the Census Bureau calls "non-family households." He interprets this to refer "primarily to gay or heterosexual couples cohabiting out of formal wedlock." This, however, is not so. As the Survey's tables show, 82% of those non-family households – some 30 million households altogether – are people living alone.
Put another way, of the 50.2% of American households that do not include a married couple, more than half are single people living alone. And one thing we know about single people living alone is that the overwhelming majority of them want to get married, and the large majority of them will someday.
So, yes, most American households now do not include a married couple. Does that mean marriage is on the outs? No, it means America is a very rich country. In America, 30 million adults – 10% of the total population – can afford to live by themselves. But they don't want to do that forever. They want join their single household with another, and join the married majority of adults.