The Transportation Security Administration is planning by the end of the year to launch something called CAPPS II—the Computer Assisted Passenger Prescreening System II. It's a computer system that scans information on would-be airline travelers, cross-checking a plethora of public and private databases in order to assess your security risk. Airlines, with the government's help, will be able to consider your credit rating and driving record when deciding whether to let you on a plane. The TSA currently insists that only security-relevant material will be considered. Since airlines apparently consider what book a person is reading to be security-relevant, any available records on book purchases should perhaps go into the CAPPS II mix.
Many people seem to worry more about supermarket club cards than about the government having ready access to every possible bit of information (and, of course, misinformation) about you. In the past year we've seen that even private databases all too often end up in government hands, used for government purposes. The worst thing that a private enterprise is apt to do with information on your interests and buying patterns is target ads at you; government agents might target you for far worse reasons.
We may be doomed to live in a fishbowl by the inevitable expansion of database and surveillance technologies. If so, we need to be constantly vigilant about who might really be trying to stick a hook in us.