The Facebook IPO, valued at tens of billions of dollars, is going to make some people very, very rich. Where does this incredible value come from? From the personal information that the millions of Facebook users willingly provide the dominant social networking site. Most of that data will be used to customize advertising designed to appeal to Facebook users. Every time you click on an ad, indicate a preference for anything, Facebook knows, and advertisers hungry for your business will know, too. Other folks, with potentially more sinister motives, are able to use the information, as well. Prospective employers, for instance, can discover things you didn’t include in your resume, and anyone else who might want to find out more about you, for whatever reason, will not find it hard to unearth your not-so-secret secrets. Big Brother may well be watching, and he certainly isn’t the only one.