Even though, I myself do own a facebook. I am absolutely against the use of it for my children in my house until age 15, with one rule... You friend me. I know my way around a facebook page, therefore most parents who have their children added do not know, that there are specific settings where children can actually block certain content from just YOUR sight. Suppose one of my kids had pictures up from a recent party, they can go to edit settings on the album they posted it in, and changed it to "friends only" and then there is that "except...." button. There they can type in MY name and click save. DONE. I will never be able to see that album. So I do a 1-2 time a month "check up" where I have my kids log on, skim through everything, and tell them to show me something that I think looks suspicious. I have a 14 year old, who begged me to get a facebook, so I let him, because his grades were marvelous last semester, but... I had him give me his login information, since he is younger, and more naive. I want to keep an eye out on him from the random people who sometimes even add me. There are so many things to watch out for on facebook. I've seen some pages of kids, their statuses are about drinking, smoking, parties, ext. They have crude, sexual pictures, girls making out with out girls, its very hard to keep track of the 400 or so people that your teenagers have added. It's a hard site, but I've allowed it in my house, because I myself use it, keep a close eye on your kids if they are on this site. And make sure you know Facebook better then your teenagers, I recommend every parent of a kid on facebook gets a facebook themselves.
What other families should know
Too much violence
Too much sex
Too much swearing
Too much drinking/drugs/smoking
Safety and privacy concerns