Mrs. Alpinemaps' aunt is on FB. Her aunt's teenage daughter, who just went off to college is also on FB.
Now, aunt is the 'cool mom', always trying to be friends with her kids. But 18 year old cousin, college freshman, is posting about the parties she's going to, etc. And her friends are posting photos and details, too.
I just wouldn't be comfortable reading about that stuff! No thanks!
My sister's are on FB, and I'm not really that comfortable with them being friends with me. (Fortunately, I have LJ to complain about them, without them seeing it)