"Things I have done that I thought were positive:

• Have messaged conversations about issues that matter, but that were too personal for a class discussion
• Send messages of encouragement
• Send application presents (jack o lanterns, gingerbread men, christmas tree presents) just for fun 
• Check status changes.  Sometimes I can follow up on a student's well being the next time I see them, on the sidewalk, in my office, or before class starts.
• Use the messaging feature for my class groups to announce things like changed due dates (which are also announced through the usual channels)
• Participate in student run groups as a contributing member
• Find out things about who my students are and what they are concerned with that make me see them so much differently.  I have always been bemused by students who, even at the end of the semester, did not know my name (and I generally teach small classes with a lot of interaction!).  I can see how professors would really not know much more about a student than what they look like, how they write, and where they sit!  I was never satisfied with that, because it meant that I had never made a real connection with the person AS a person.  Facebook gives me many more cognitive "hooks" to use in making our relationship better and to help me tailor my teaching methods."

and misuse:

"I decided that,  if my students were gracious enough to be friends with me, I probably should not:

• leave a message on their wall asking why they were not in class or where an assignment was
• send them any apps without checking them first (sometimes the adverts at the end turn out to be something I would not like to endorse personally)
• be judgmental about any activities, even if I initially find some of the posts/photos to be surprising"