I just joined, after a year or so of 2 friends (in real life) bugging me. You don't have to put your relationship status or any of the other things mentioned.
I don't see how people consider 175 people to be real friends. So far, I have 13, and all are people in my family, or old friends from AZ. There were quite a few listed that "could" be my friends, according to Facebook, but when I searched through all 300 (so it seemed) of them, most I didn't know and quite a large minority were people who were friends of my older son in preschool in AZ! The connection was the daughter of one of my friends there, who I did add to my list.
I rarely make a comment. Just don't feel the need to tell people what I am doing every moment. But, I do read what others say. Part of the reason is that as a future therapist, I don't want my clients knowing about my personal life. No pictures up there, either, mostly because I don't know how to do that. But, I really don't want to put any up anyway.
I don't Twitter or text message. I do use IM and I do have a cell phone, but I only put it on when I need to call someone, or when I am going to be out for a long time. Most of the time now, when I am away from home for hours at a time, I am in class, so it's not on. I don't have it on when I ride, unless I am leading or with a group that needs to stay in communication.
I've overheard some moms of teens and kids in college that they feel this is a way to keep in touch with their kids. I feel it's just another way for them to be "helicopter" parents. I didn't want to know everything my kids did! They communicated frequently enough.