bloody hell, everyone is so damn paranoid... "They" are not out to get us. "They" couldn't organise a piss up in a brewery... as demonstrated by the (North) American government falling apart this week.
Long ago, I was perfectly happy being paranoid. I knew it so I felt secure in the fact that it was probably just my imagination. Then a friend pointed out "Just because you're paranoid, doesn't mean people AREN'T out to get you"
Seriously though, I'm down on facebook/twitter for why most people use it and how it's used, not data wise.
If you want to worry about someone, worry about google; they track you multiple ways (they have a huge hash with mac addresses against searches). I found 'my' search history in my google account and it had searches from machines that pre-dated the actual google account. At first I was laughing, thinking "what a dork" that I was looking up, then I got the creepiness about it. I turned it off and 'deleted' my data, but it's there.