Regrettably there are numerous, well documented cases of Facebook doing exactly this. They've literally been taken to court over it several times (look into "Sponsored Stories," "Beacon," etc).
Even if you don't use it, they have a shadow profile of you over there waiting, with relationships pre-graphed, simply by virtue of being in friends' contact lists who do.
The site "Likes" things on peoples behalf just because they talk about it (even negatively!) with others. It occasionally automatically "friends" people because you looked at their profile and mutual friends in common. It constantly takes liberties with people's relationships, friends, and preferences, without asking. The mobile app turns on the damn mic to listen to ambient noise in the background so it can try learn what you're listening to or watching on TV!
None of this is to try to convince you to care or take up the pitchfork against Facebook, but they're not like other sites. Harvesting your contact info from your friends phone to add you to their graph is an invasion, in my view (glib app permissions dialog, notwithstanding).