It's disturbing how much social networking systems are the center of all attention right now. It's like the keynote speech that I've heard on last year's SIGIR: the way you see the world will change, because everything you do and everybody you meet will be transparent to everybody without them having to ask you for it. I've talked about this in the past. But some people are taking this concerns to a different level:
In Facebook's Brilliant but Evil Design, Joshua Porter points out that because Facebook ulterior motives are financial (they can tell what, out of the things you've done, should be told to your friend because it will generate more money to them), the experience sharing might actually hurt your social status. And because you don't have much of an option with all the great "you are opted in by default" behavior of social networks out there, you can't really control it.
Makes me a little scared to tell you the truth. Our society is changing in front of us. Initially, we were exposed to product ads based on word of mouth only. So things that came to you were filtered by your friends based on their experience with it. Then came the newspaper, radio and TV, where everybody would be exposed to ads that were considered effective to a large population. It was a very messy "weapon". But we had still the word-of-mouth to filter out this mess and still give you good suggestions.
Now we are moving towards a world where word-of-mouth is being automated for you based on what is more likely to affect you. It doesn't mean that it will always give you bad products. Not all products will be using the fact that you like to buy things with shiny boxes. But it will increase the noise in the word-of-mouth channel. Then what is next?