Last Sunday’s New York Times Magazine cover story “Are Your Friends Making Your Fat?,” posed some intriguing ideas for social marketing campaigns.

The crux of the social contagion theory: friends and even friends of friends can have an enormous influence over your health habits and other behaviors. So why not, for example, combat obesity by urging people to diet with their close friends?

Easier said than done. But there are promising applications of this theory in the works, according to reporter Clive Thomson, who describes an effort by researchers at the Schroeder Institute for Tobacco Research and Policy Studies to develop a Facebook app for people trying to quit smoking. The app allows them to publicly post how long they’ve gone without smoking and how much money they’ve saved.

By going public, the theory goes, you’ll inspire and influence others to quit smoking, too.

Going public also creates accountability. In “Julie & Julia,” the Amy Adams character takes on the challenge of cooking all 524 recipes from Julia Child’s cookbook in one year while chronicling it all on her blog. It’s her growing readership that goads her through the toughest tribulations. I’ve often thought wedding ceremonies – beyond the pure celebratory aspects — perform the function of holding the bride and groom accountable to the larger group of family and friends who witness the marriage.

What’s more powerful than a word-of-mouth campaign? A campaign with built-in accountability. It’s a tougher ask, but in our social media era where many people are connected online and accustomed to sharing the intimate details of their lives, it may be easier to achieve than ever.