The Pew Research Center reports that 22% of wives now make more than their husbands. This is up from just 4% in 1970.
Women have increased their education level dramatically in the past generation. This seems to be the main cause of their big jump in wages. More educated people are more likely to marry, so educated women are more likely to be wives. Less educated women, by contrast, are less likely to marry than they used to. Couples in which less-educated women make less than than their boyfriends, even cohabiting boyfriends, are now not in the married chart.
Still, I think it is safe to say that there has been a real rise in the proportion of couples in which she makes more than he does.