I've just read (and recommend) this excellent short essay by Betsey Stevenson and Justin Wolfers on the evolution from productive to hedonic marriage. Here's an excerpt:
So what drives modern marriage? We believe that the answer lies in a shift from the family as a forum for shared production, to shared consumption. In case the language of economic lacks romance, let’s be clearer: modern marriage is about love and companionship. Most things in life are simply better shared with another person: this ranges from the simple pleasures such as enjoying a movie or a hobby together, to shared social ties such as attending the same church, and finally, to the joint project of bringing up children. Returning to the language of economics, the key today is consumption complementarities-activities that are not only enjoyable, but are more enjoyable when shared with a spouse. We call this new model of sharing our lives “hedonic marriage”.
Read also the lead essay on 'the future of marriage', by Stephanie Coontz, which takes you through a concise history of the marriage institution and its role in society.