Babies born to Unmarried women - 40% in 2007

This was a hard-to-believe statistic I learned from the latest Data Brief issued by the National Center for Health Statistics. Of all babies born in 2007, 40% were to unmarried women. The percentage is rising among all age groups, not just teens; it's rising even in women 25 years of age and older. For example, the birthrate for unmarried women between 30 and 34 years old was 21 per 1000 births in 1980. By 2006 it was 55 per 1000 births.
That doesn't mean that Daddies aren't around, of course. But is it the Brangelina effect; or is it the greater economic independence of women and reluctance of men to have children; or is it the continued existence of a marriage tax that is undermining the institution of marriage?
I'm not sure how bad this is for society, if at all. Just don't know the evidence to comment. But it sure did surprise me.