On Friday, the Times reported on a set of married couples in which the partners lived in different cities, sometimes different continents altogether. The Current Population Survey data they cited categorized some 3.8 million people married but with spouse absent in 2006, compared with 119.1 million married with spouse present.
The article cites Skype (and telephones) as a key method of staying in touch across vast distances. It also discusses requisite changes in parenting strategy. The absent spouse typically becomes the "good cop" with the kids.
It's hard to know whether living apart is a trend, as the title, "Living Apart for the Paycheck," seems to suggest given the current economic bad times. But anecdotally the prevalence of physically separated spouses on the academic job market certainly seems high. Many of the couples in the article include academics.