I have added many colleagues as Facebook friends, including former bosses (as far as they have a Facebook account and want to share their information with their colleagues, including me).
I don't post very confidential things on Facebook and other things are not about work. When there is a personnel party, I will post about in a positive way. No (negative) gossip about a specific colleagues, but when I do a Facebook check-in, I will tag my colleagues that I saw at that party as far as they have a Facebook account.
Some colleagues at school have students as Facebook friends. That is not my cup of tea. I won't share Facebook information with students, like some other colleagues do. A while ago my boss told other colleagues (and me) not to make online contacts. Most of the people have forgotten that, but I still remember that, and adhere to it.