Facial recognition software is now in wide use by groups as disparate as Facebook, local police departments, Homeland Security, and the NSA. What it means is that whenever you post a picture of you, family, or friends anywhere online, someone can easily identify every single person in the picture, and very likely determine from the caption or comments where you have been and what you are doing.
That information, if scooped up by a private entity like Facebook or Google, is immediately sold to advertisers. Lately, I've noticed that the ads being served on Web sites I am browsing change within one or two minutes of doing a search on Amazon or some other shopping site. It used to take a day or two for me to see those changes.
We are trading privacy for convenience. It remains to be seen how this will all turn out, but Big Brother is really twins: Government Big Brother (all the local, state, and Federal agencies collecting and maintaining data on us) and Business Big Brother (all the large multi-national companies, like Google, Amazon, and Facebook that collecting and selling our personal information).