Unless you've been living a Luddite existence "off the grid" in a cabin in the Rockies for the past few months, you're probably aware that there have been a number of revelations about just how much monitoring the NSA is doing of US citizens in the name of "national security". Leaks about NSA intelligence-gathering programs have sparked intense debate about the conflicts between individual and social liberties, and protecting the nation from potential attack--and that is a healthy debate that we, as a people, should engage in regularly just to keep things in check. Meanwhile, though, our data and online activities are also being tracked and monitored by private companies, and not to defend against terrorism.
Does that make these companies evil? Not necessarily. When you share information, it provides Google, Facebook, Amazon, and others with important data they can use to identify patterns in usage and behavior. The more data they have, the better they can scale their data centers, and optimize their servers to handle the demand. The more data they have about you personally, the more they can tailor the ads that are served to you, and cater the online experience to uniquely fit your interests, and the way you use the Internet.
You need to be aware of how your data is being used, and companies should be open and transparent about what data is being gathered and how it's being used. You should have the ability to opt out, or security configurations that allow you to exercise some control over your data--so don't let your guard down. Protecting your own privacy and personal data can be a full-time job, and it becomes even more complicated when Yahoo buys Tumblr, and Facebook buys Instagram and suddenly your data is being shared, merged, and integrated in new ways you hadn't considered.
Next time you think about government monitoring activities, and whether or not those actions infringe on your privacy, though, you might want to consider the fact that you've probably already willingly shared far more information, with far more companies than you're consciously aware of. Truth be told, for many people there isn't much left that "Big Brother" needs to spy on, because the information is already available to the general public.