I just got around to reading Tyler Cowen's New York Times column about how divorce has actually improved the quality of married life around the world. Can't say I've had much personal experience with the subject, but he brings up a lot of good points. This seems especially crucial:

And what about the children? Don’t they suffer in happiness and future prospects from divorce? Maybe so, but Mr. Wolfers and Ms. Stevenson do not think the question has received a final answer. To be sure, it is better for a child to have happily married parents, but when the family is dysfunctional anyway, we don’t know whether divorce harms the children.

Right. It's easy to point to studies showing that children with two married parents are better off than those without (although, as Trish Wilson has pointed out, even that research is ambiguous at best). But that's not even the relevant comparison. What you'd need to do is look specifically at children in broken marriages and figure out whether they'd be better off if their parents separated or stayed together. In many cases—say, one of the parents is abusive—staying together will obviously be the worse alternative.

As far as know, no one's ever done that, and so no one really knows if, on average, divorce has been bad for children. Maybe someday Steve Levitt or one of his acolytes will stumble on a clever natural experiment and settle this question once and for all. Maybe not. In any case, Cowen notes that "the number of children in a given divorce is, on average, declining," which seems like a positive trend.