> How might this be used against me in the future?
I was already doing that, but because "The Internet never forgets", not because of surveillance.
Or in other words, I've already assumed either outright surveillance from the ISP or the botnetted-computers my friends/family use to go to visit my Facebook crap, or later database breaches/hacks conducted by criminal elements.
I mean, all you have to do is look at /r/cringepics, "lamebook", 4chan, etc. etc. to realize that people actually are watching what you post, commenting about those things you post (in forms easily queried by Google) and those people don't work for NSA (who in any event can neither retain the entire Internet indefinitely, nor actually look at everything that's captured even if they felt like it).
So watch what you say if you feel you must, but I don't see why NSA in particular would cause a shift in your behavior, if having things you said come back to bite you later is something you're worried about as a concept, you've long had reason to be concerned.