Ironically, Unions urge you not to have students, present or otherwise, or their parents as well as facebook "friends." If you use etiquette in what you post, I don't see the problem. I see positives in the respect that knowing I am lurking around makes them aware of what they post.
I have used Smarthistory in my French classes and thought I would share...
It is a multimedia art history web-book that trumps the traditional textbook.
Enjoy!