In their attempt to prosecute a used book seller for tax evasion, the feds tried to get a hold of Amazon.com sales records, including identifying information for 24,000 customers. Later they scaled back their request, asking to violate the privacy of only 120 individuals (oh, that's better).
As Crocker stated,
It is an unsettling and un-American scenario to envision federal agents nosing through the reading lists of law-abiding citizens while hunting for evidence against somebody else.Between this and the unflinching stance of librarians against certain sections of the U.S.A. P.A.T.R.I.O.T. Act, the people of this great nation seem to agree: reading is private.
Though if you want to shout from the rooftops that you enjoyed my books, feel free.
The key word there is "free."