If you were a regular user since 2005 and leave now, it does not make any
difference anymore. The collected data about you is enough to interpolate
your profile for the next decades.
Does it really matter if you have been on facebook at all? Even if you never
joined, people upload their addressbooks with all of their contacts, they
upload pictures of people never been on facebook and tag them (and share other
information about everyone, which facebook probably is able to use as well). So
essentially facebook builds your social graph no matter if you have ever been a
member or not.
It does make a difference. Just not to care and to give up is no solution
either.
Right exactly. I don't have (and have never had) a Facebook account. But I know that they have much more information about me than I would want them to. They most certainly have some sort of "shadow" account sitting there associating whatever they can to it; friends' address books, photo tagging, etc.
And if you throw in the Instagram wildcard, it gets worse. I signed up for an Instagram account before Facebook purchasing them. I never posted a photo, but I'm sure this still adds to the reach of their shadow profile. People who actively use both Facebook and Instagram, I feel sorry for them.
I do use twitter and google extensively though, so I guess I can't complain or say anything about my social profile. Twitter luckily has a smaller budget, so they can't quite crunch data as hard as Facebook can. But Google owns me, I'm afraid.
I'm not (too) scared about NSA. At least, NSA has some sort of government bureaucracy that slows down their ability and interest in my data; they aren't trying to use me for-profit. I think we should be more scared about what Google, Facebook, Twitter, LinkedIn, et al. can do, especially because they are generally bound to whatever their current (and fungible) terms of service and privacy policy stipulates. [edit] i.e. policies written for the sole benefit of the share-holders.
It does make a difference. Just not to care and to give up is no solution either.