I use it a lot like most people do. I share some thoughts and comments. I share news articles and I often share funny pics that other people, groups or pages post. I share some funny clips and trailers of upcoming movies that I think would be awesome and ofcourse I share my favourite music videos.
Some people only add their close friends in real life, cousins, uncles, aunts and other relatives who they are close to as their Facebook friends. This is a close section of people and means secrecy is involved. There are usually few surprises and arguments because these people know you well and they expect or share several of these ideas and views of yours. I on the other hand, like a lot of people on my Facebook friends list, add a lot of people I have never met in real life before but have met and become friendly on other Facebook groups, blogs, Twitter etc. The problem here for some of us is that these people will only share one of our interests/views but do not have the same interests or views in several other things.
It depends, sometimes you make a lot of good friends that way and they remain friends for a long time while others end up pissing you off or unfriending you because of things you disagree on and say nasty things about you when they get upset.
Prompt from The Learning Network at The New York Times