Facebook users aren't just connected to real-life friends; their online "friends" also include relatives, coworkers, former lovers and others.

And that can be stressful, since including these others brings aboard some people who aren't amused by your online persona. A UK study of 313 Facebook users, most of them college students, finds that their "friends" are drawn from an average of seven different social circles—and that the more social circles, the more likely this burgeoning online coterie was a source of stress.

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