Facebook’s default approach—sharing with everyone in your personal network—has created a dilemma for professors whose students want to be their online friends. Often the students inadvertently share their party pictures and other private material with their instructors on Facebook, giving some faculty members the feeling that they have crossed too far into students’ personal space. Professors have also accidentally shared comments with students that they meant only for fellow instructors.
—Professors Consider Classroom Uses for Google Plus – Wired Campus – The Chronicle of Higher Education.