To Friend or not To Friend

Ewan McIntosh responds to a tweet that asks if it is ok for teachers to have Facebook pages.  He responds with an astounding, "yes."  The question then becomes, do we allow our students to 'friend' us?  He responds with even more astounding, 'no!'  His advice is to start a facebook pages which is a Facebook page for a product or service.  The idea is that you could have a class page or you could set up a less personal page so you can be friends with your students in a way that has more boundaries.  Facebook in the class room makes sense to me.  The other point raised is that teachers are very similar to clergy in the sense that they live under a microscope (I'm currently clergy).  Everything we say and do is judged on that basis.  So in that regard, we must be ever so careful what is posted, in the event that it ever were to be made known to class (or congregation).  So my questions are: what are the policies regarding Facebook and/or other social sites in any public or private schools?  Are any teachers friends with their students?  Are they any stories where a teacher/student Facebook friendship went well?