Wow. this Q&A is so rich with good information it’s hard to know what to point out. Check this out:
More and more, your data isn’t under your direct control. Your e-mail is at Google, Hotmail, or your local ISP. Online merchants like Amazon and eBay have records of what you buy, and what you choose to look at but not buy. Your credit card company has a detailed record of where you shop, and your phone company has a detailed record of who you talk to (your cell phone company also knows where you are). Add medical databases, government databases, and so on, and there’s an awful lot of data about you out there. And data brokers like ChoicePoint and Acxiom collect all of this data and more, building up a surprisingly detailed picture on all Americans.
Really, read the whole thing.