Social Networking Addiction - Is it becoming a disease?

Seems like kids these days are glued to their cell phones, and if they're not, they're preoccupied with online social networks. There is no actual medical diagnosis of "social network addiction", but therapists are seeing more and more cases of people who have their online social lives ravage their existing social lives, relationships, family and work. For example, the online community Second Life has become a damaging addiction for many, and some spend over ten hours a week on Facebook. My concern is with children developing unhealthy social networking habits that parents dismiss or fail to recognize.

How do you go about diagnosing social network addiction? What are the symptoms?

As educators and parents, what do you think we need to do in order to prevent kids from becoming social network site addicts?