According to an article in Baptist Press,
The survey of 1,000 randomly selected Protestant pastors found that a majority (58 percent) will perform weddings for couples they know are living together. Nearly a third (31 percent) will not, and 10 percent are not sure.
When it comes to cohabitating couples, pastors who consider themselves mainline are more likely to perform weddings then those who consider themselves evangelical.
On first reading, this struck me as an obvious choice, but on reflection, there are some subtleties. What do you think?