They absolutely have used section 215.
For example, a survey conducted by the University of Illinois suggested that, by December 2001, the FBI had already approached 85 out of some 1500 libraries.
http://www.aclu.org/Privacy/Privacy.cfm?ID=11054&c=130 In May 2003, in testimony before members of Congress, assistant attorney general Viet Dinh said federal agents had visited about 50 libraries.
http://www.lawrence.lib.ks.us/policies/patriot.html According to the article, "in a survey last fall of 465 public and 120 private libraries in Illinois by the Library Research Center, seven public libraries reported that they had received requests for information about patrons or circulation records from the FBI, and 17 said other requests came from police or other agencies. Eight said the reason given for the requests was a national security investigation…. Though the survey did not ask whether a Section 215 order had been presented, 14 libraries declined to answer some survey questions for fear of violating the law.
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