A forthcoming study by Maggie Gallagher and Douglas Allen, previewed in Newsweek, estimates that no-fault divorce laws added 10% to the divorce rate beyond what we otherwise would have had. They found that the big direct effect -- adding extra divorces -- came in the first ten years. Since then there has been an indirect effect in the couples who cohabitate but avoid marriage due to a heightened fear of divorce. This leads to further misery, as cohabiters break up at even higher rates than married people do, and cohabiters who later marry have an even higher divorce rate than other married people.
In her earlier book with Linda Waite, The Case for Marriage, Gallagher had reported that no-fault added 6 to 7% to the divorce rate. This new report is based on more and more recent studies.
I will have more details when the study itself is released.