This article reminds me of something I saw on Law and Order a couple weeks ago that caught my attention when the cops were able to use a suspect's library records to get a search warrant for his apartment.

See:
Big Brother is watching you read,
by Christopher Dreher for Salon. (Thanks, Josh.)

Tattered Cover's ordeal began in March 2000, when the Adams County District Attorney's Office contacted Meskis to inform her that the Drug Enforcement Agency was planning to subpoena the store for one of her customer's sales records. During a raid of a methamphetamine lab in a trailer park in suburban Denver, authorities had found an empty Tattered Cover shipping envelope addressed to one of the suspects in an outside trashcan, and two nearly new books, "Advanced Techniques of Clandestine Psychedelic and Amphetamine Manufacture," by Uncle Fester, and "The Construction and Operation of Clandestine Drug Laboratories," by Jack B. Nimble, inside the trailer. The DEA planned to strengthen its case by tying the suspect's illegal activities to his purchases of books outlining how to make methamphetamine.

Meskis answered that such a request was a violation of First Amendment rights and said she would fight it in court. "I thought that was the end," she recalled, "but it wasn't." Instead of bringing it to court, the DEA persuaded a judge to authorize a search warrant, which would be immediately executable and would bypass judicial interference. That's how the five task-force officers wound up in her bookstore.

Meskis' first try at quashing the warrant wasn't as successful as she'd hoped. In October 2000, a Denver district court judge narrowed the warrant's scope but ordered the store to turn over the information. She appealed that ruling to the Colorado Supreme Court, and on Dec. 5, 2001, lawyers from both sides presented oral arguments. The decision is expected sometime this spring.