I have 2 personal experiences I can share of FB getting people into trouble. Both of these folks were in their early 20's and, through the eyes of seasoned adults (like us) might appear as just stupid kids. But I think you can clearly see the difference between the two examples. Either way, though, the end result is the same.
1. My step daughter's boyfriend ("Joe") wrote on his FB wall one day after a particularly long and tiring day, "Man, sometimes I hate working." The next day he walked into work and was pulled into the boss' office where he was told "You don't like working? Congratulations, you're fired. Get out." He had no idea what happened until the next day when one of the guys that was there before him the morning before over heard one of the other mechanics ("Steve") showing the boss something on his FB wall. He was real life and FB friends with Joe and so Joe's post was visible on Steve's wall. The boss saw that, didn't look for or ask for any context and decided that he was going to teach 'these damn kids' a lesson and make Joe the example that he'd been looking for. Joe didn't hate his job. He was tired from working several long days in the summer heat.
2. We had an intern at work call in sick for 3 days claiming that she had pneumonia and was in the hospital. A quick look at her FB wall by one of the other interns (with whom she was FB friends) showed her on the plane to Aruba, on the beach in Aruba, in the club in Aruba and finally, on the plane home from Aruba. That last picture was captioned "What work doesn't know won't hurt me!" She was let go as soon as she walked in the office the following day.
My personal rule with FB or any social media is this: If we work together, I will not be connected to you on any social media platform. Period. If we were friends before and you come to work were I do, I will (and have) sever those connections. Not because I post anything that I'm worried about but because of the case of my first example - someone not seeing something they like, out of context and making decisions based on bad or partial data. Life will stack itself against you of it's own volition & nature... there's no need to help it along