My dad is a retired educator who is now on a school board. The first three years he was on a board, most of the board members didn't know what Facebook was. Finally, some younger people have been elected and they are finally starting to address this problem. Granted, in the last four years, two male teachers have been fired due to inappropriate relationships with students.
My mom is a retired teacher too. I've talked to both my parents and they have said that they used to feel uncomfortable when they would see students in restaurants. My dad had a rule that he never went to a bar in the town that he worked in, because he never wanted a student to see him leaving a bar. Because that would quickly become a rumor that he was drunk and that would become a rumor that he was drunk driving.
Now, teachers and students are friends on Facebook and most people are idiots when it comes to posting stuff on Facebook. Mrs. Smith may not think it is a big deal to have a folder of pictures from Spring Break 2006, but those pictures wipe out the idea that there is any difference between the teacher and student. Once that happens, anything is possible.
I would love to see a psychological study that focusses on how different our behavior is behind the "walls" provided by Text messages, IMing, and email versus what we would say face to face. I think the loss of that immediate reaction makes us willing to say things we would never say otherwise.
(I also want to make my standard point that I find this entire thread uncomfortable).