Didn't realize how this thread topic winded its way on other side topics in addition to one's current reading.

Public libraries, if they implement their policies properly, do take the issue of their patrons' personal info. as confidential quite seriously. So seriously that the (national) American Library Association had to take a strong public and defensive position that their patrons' reading list and personal info. was not immediately available to the police for investigation..I think the U.S. federal Terrorism Act enacted after 9/11, ignited this whole debate. Why? Because obviously what you read does not reflect your personal preferences or beliefs. One reads on a topic to be informed but not use the information to hurt others.

I think there were some situations where the a public library was challenged by the police to handover the info. on a client.

Princess,I would consider the library card...a record. It is record that has discrete identifiable pieces of info. on it: the name of the library that issued it and bar code which is like (but does not have the same legal weight) your government ID. It is a valuable record since one is held responsible for fines, etc.

As for storage of your reading preferences by the library system: most library software over the past few decades do have this feature, but many public libraries may not choose to activate the feature extensively or at all for several main reasons I can think of:

a) issues of personal information tied to reading preferences
b) technical problems & computer server memory required to store history reading list info. for thousands of library users
c) how many users would actually use this/know how to get into the feature? This latter feature believe it or not, is yet another feature to teach library users. Libraries are more focused and rightly so, on teaching people how to construct proper database searches across different types of databases that the library buys license plus its regular library in-house catalogue database.

Having said all of the above for public libraries: things are quite different for corporate libraries and some university libraries: since user group is small, usually adults and users are employees with/aligned with the parent organization, the user can be taught and does use some specialized database features to store their reading lists or store search keyword strings. Often software is designed so that only the user, not library, sees their search strings, reading lists, etc.
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In response to what Mountain Ash's library was offering: Keep in mind the library is offering only self-help book/info. AFTER a client received diagnosis from doctor or psychologist.

I have developed and imposed specific service policy in training library staff, where they were trained that the librarian and any other library staff member, was not in the business of attempting to diagnose a: medical, psychiatric, legal or financial problem.

We tread a fine line between diagnosis of a problem (with legal/medical risks) and provision of info. But an experienced librarian does know when not to cross the line and instead make a referral to the client, to seek other trained professional help of a doctor, lawyer, accountant, engineer, etc.