This article is quite interesting, as the Facebook trend has traveled to middle school students, and I see my fellow teachers friend students, and others completely avoid the students.
I think facebook is a very hot topic at this point and there is no clear guidelines on the proper etiquette for a teachers social networking with students.
I personally find that this is too thin of a line to stand near. A teacher should not necessarily be friends with their students, but to show compassion also shows the students that we genuinely do care for our students. But with so many issues surrounding the relationships between teachers and students, I believe that it is best to keep the personal aspect out of the teacher/student relationship.
I could see how facebook could be a good tool for students and teachers to connect in terms of homework assignments, due dates, and questions that might arise while working on these assignments. I have considered creating a "Group" page devoted to my math class, yet not linked to anything outside of school related concepts. It could be a great tool to let the students come together and ask questions towards the teacher or one another, and to help with reminders of events coming up in the class.