It's not so much "get out of fb" it's how you use it.
"but but but it's your privacy!!111" yeah, exactly, that's why I limit the information I share with FB, no location checkins, no "picture every other minute", no "fill your missing data" BS, etc
Also, don't install or use the FB mobile app (good thing it sucks)
There are browser extensions that hide G+/FB/Twitter buttons, it's a good idea to use them
" Even if you never posted anything, they can easily work out your age, gender, sexual orientation and political views. "
Why is this being said with a surprised tone? Oh and this happens in real life too, you don't need fb for that.
"Guess your age and gender"? People on the street can do that too, I better walk with a paper bag over my head.
But there is no one person on the street that can do that for all other people on all the streets on the planet. Concentration of information in one "brain" is the problem, not that not everything is top secret. There is a difference in the possible consequences between some neighbour on the street seeing you and someone having a database of all public movements of all people.
Edit: and that's what I find most troubling: that someone can know much more about me than myself. Things that you can only realize from looking at the data over time, things that are invisible when experienced on real time.
I imagine the synthesis of these forces in the future is technologies that aggregate, but that the indivudal can buy into. Do you want help deciding what to wear based on the weather or time of day, beyond what your assistant can do for you? Then there's a collective data channel you can opt-in to joining, and you'll trade some of your personal private information for access to a digital "collective unconscious" of aggregate data. I liken it to the 23andme approach of collecting genetic profiles.