Social websites make money off of selling your information to internet tracking companies for trend analysis, data mining, personal profiling, and all sorts of things like this.
I'm actually shocked when I see some random shmoe actually surprised that "facebook doesn't care about my privacy omg!"... guys, you're voluntarily giving your personal information and information about your "friends" to a corporation. Even when you select going "private", which I hear a couple of my friends claim so smugly, is all they need and they'll be fine. Wrong, your information will be, and will forever be, at the mercy of internet companies, companies, malicious users, the government... and pretty much anyone else interested in your information.
To be totally honest, I'm all for companies looking you up on facebook when they want to know about you for a job. If I'm going to hire someone, you bet I'll be looking for information they willingly gave to the entire internet to know about things I couldn't ask about in a formal interview (likely because it's against the law). I've heard countless times people "don't know why I didn't get that job"... then look them up on facebook and you see tons of party pics, alchohol, drugs, you name it...
"But I set my stuff to private!" is a ridiculous false sense of security. Everything you put on the internet can be found, tracked down, and exploited by someone with enough know how and motivation. I've seen countless reports of people "hacking" other people's facebook pages and guess what happens?? All that "private" information you thought you had is out the window.
Now, I'm not saying exploiting people's information is always a bad thing. As a corporation, I definitely want to know about potential customers, demographics, trends, what's popular, and all that stuff so that I know how to target marketing efforts and make the most money I can possibly make. For these reasons, people (like facebook) sell your information to these people, it gets compiled to data lists that are used (or resold to other companies) so that tons of people have some, most, or all the information about you. It all started with you voluntarily giving information up about yourself.
So, who owns your information? Do you? Do you even know how many people in the world have your information? Do you care that people know what your lifestyle is? What interests you have? If I'm a company and I bought an internet mailing list per se, I would believe I own your information and I could do whatever I want with it, including selling it or giving it to subsidaries...