As previously mentioned, the USA PATRIOT Act allows federal agents to access your book buying or borrowing records, without anyone ever informing you. Section 24-90-119 of the Colorado Revised Statues is not especially encouraging:
(1) Except as set forth in subsection (2) of this section, a publicly-supported library shall not disclose any record or other information that identifies a person as having requested or obtained specific materials or service or as otherwise having used the library. (2) Records may be disclosed in the following instances: (a) When necessary for the reasonable operation of the library; (b) Upon written consent of the user; (c) Pursuant to subpoena, upon court order, or where otherwise required by law; (d) To a custodial parent or legal guardian who has access to a minor's library card or its authorization number for the purpose of accessing by electronic means library records of the minor. (3) Any library official, employee, or volunteer who discloses information in violation of this section commits a class 2 petty offense and, upon conviction thereof, shall be punished by a fine of not more than three hundred dollars.
Well, subsection (2) pretty much leaves the door wide open, now doesn't it? You can be sure that when a federal agent requests (requisitions?) your book borrowing records, any Colorado library will need to comply, despite nice-sounding statements that "your records are strictly confidential". Perhaps some Denverites who really care about patron privacy need to join the Library Commission. (Either that, or it's time to start a library that isn't publicly-supported, since it's clear that he who pays the piper calls the tune.)