In the past, if the government wanted to keep tabs on someone, it took considerably more time and resources than today. That's because today, people willingly give up their right to privacy when they 'connect' with Facebook and everything they post under your Facebook alias can be traced back to them.
'That's not so bad,' one might thing. 'I'm an honest-to-goodness American (or European, or Asian, or wherever-else-ian) with nothing to hide!' Power to you, brother (or sister), but let's say your government has reasons to suspect you. Maybe they think you make bombs in your basement, or you starve your dogs, or torrent kiddy pr0nz. Why they suspect you doesn't matter, really (let's just assume your neighbor secretly hates your guts and sent an anonymous tip to the police). What does matter is that from said anonymous tip onward, your life is under scrutiny. (Sometimes, it doesn't even take a tip; apparently, if you're Arab, you're already a suspect in certain-countries-we-won't-name.) And the whole thing can seriously snowball from there.
Let's pretend you used your Facebook account to 'connect' to Yahoo! News, which you prefer to clunky newspapers that are bad for the environment because OMG global warming, think about the trees, etc.* There's an article about terrorists born and trained in your country, and you feel a burning need to state your opinion. Let's assume you type, 'lol ne1 can make a bomb just goodle it doesnt mean your a terorist' (or, if actually care about not sounding retarded, 'Anyone can make a bomb, information on how to do it is all over the net, but making a bomb doesn't mean you're a terrorist').
This will raise a bunch of red flags to the people keeping tabs on you. Is that a harmless opinion, or did you actually feel the need to make a thinly-veiled allusion that you're building the next Fat Boy in your basement? Cue tighter surveillance, and maybe a visit from the not-so-jolly men in black at some not-so-distant point in your future.
Is this paranoia? Not really. The FBI collect social media data (surprise, surprise...) so it's not a stretch to think they'd act on it too... and the same applies to many other national intelligence agencies the civilized world over.
Bottom line: don't be a sheep. Don't give yourself up to Big Brother. You have a right to privacy; don't throw it away, even if everyone else is doing it.
* Generic hippie rhetorics here.
