This week I will be working through a new book, William Eskridge and Darren Spedale's Gay Marriage: For Better or Worse? They look at the Scandinavian experience with legalized marriage-like relationships for same-sex couples, starting with Denmark's new law in 1989. They also make sidelong glances at the experience of other countries and provinces that are experimenting with new marriage laws aimed primarily at gays and lesbians.
One of the northern European experiments in marriage alternatives has been the Dutch "registered partnership" law. Registered partners share many of the financial benefits of married life, but there is no legal expectation of sexual fidelity, and it is much easier to get out of than is a full marriage. This was created to allow a version of gay marriage without calling it that.
To everyone's surprise, though, most of the couples who have taken advantage of the registered partner law are heterosexuals. They are attracted to "marriage-lite" precisely because it is not as demanding or permanent as marriage. In fact, I think registered partnership is not so much "marriage-lite" as "cohabitation-heavy."
I know of no research on exactly what these mixed-sex registered partnerships are thinking. I have a guess, though. For many of them, I expect that she thinks it is a step on the way to real marriage, whereas he is content to have the benefits of marriage with few of the responsibilities. When they do the breakup studies of registered partnerships, I expect that all the partnerships involving men, gay and straight, will have a dissolution rate even higher than the high divorce rate.