EUGENE VOLOKH ON LIBRARY PRIVACY:

I sympathize with objections to the government gathering library or bookstore records, especially without a warrant and probable cause. Such practices can indeed deter people’s reading what they want to read.

But what about the government interviewing a suspect’s friends about what he said or wrote to them, or subpoenaing them to testify or bring their records? That would deter people’s saying what they want to say, and e-mailing what they want to e-mail — at least as much exercises of one’s First Amendment rights as borrowing a book from a library. And people are in fact sometimes deterred this way.

Read the whole thing. One big difference is that librarians and booksellers are organized in a way that conversationalists are not. That’s not necessarily bad — it’s as likely to be a sign that conversation is underprotected as that reading is overprotected — but it’s a difference worth noting.