I'm a teacher and I have a facebook account. So far it hasn't been a problem. I have all of my settings set to friends only and I rarely post anything anyways. A lot of my students will ask me if I have a facebook account and I just say no. I don't have a profile picture and I don't have a city listed as a hometown so it's difficult to identify me just from what they would find in a search. I do have one former student as a friend. I taught her in 7th grade and now she's a teacher in my school so she's also a coworker.
