I've been reasonably active in fb only for the past year or so. As usual, I have added quite a few people who were my acquintances in the past 15+ years. I had formed a certain views about their personality, based on the limited time I had interacted with them. But, some of their fb activities have been quite a revelation to me. It is like, they are quite different people with interests that I had never associated with them before. It reminded me that, just like time, fb is also a learning facilitator. Never judge a cover by the book, never make opinions abt a person without digging deep :)
On that note, some interesting research articles: Here and here.