Information Today has a very interesting article on anonymous library cards. Like a retail gift card, these cards are issued anonymously with a cash deposit and do not require any personal identification. Sounds like an intriguing concept for ensuring patron privacy and lending to out of town patrons.
From the article:
With an anonymous library card, the library is willing to loan materials to anyone because it knows it can’t really lose anything. Since the library would never loan more than it could re-coup from a cash deposit, it would be able to loan controversial items without storing personally sen-sitive information. If the user doesn’t return the material promptly, the fines would be deducted when it’s finally checked in (or once the accrued fines reach the price of the material).
Source: Library Associates LibBlog