Facebook has become an educational pain in the butt. There are lots of good arguments about why students should be educated about it, especially the privacy issues that keep cropping up. Still, I won't teach it.
The first reason, Facebook is blocked at my school. I have no opportunity to leverage it as a learning tool. I can't even use it to promote the work our students create there.
I find very little usefulness for myself in Facebook. It isn't that I am less social than others that are online, I just use other tools like Twitter. Therefor, it would take a lot of my time to learn how to not only use it fully, but to know how to make it private.
The last reason is what convinced me to not teach Facebook. I am not the parent of my students. I am tired of being the social site police for my school. Parents need to take responsibility for their own children when they are online at home.
I will still teach digital citizenship at school, but I am done with Facebook.