I've had the book for OVER a MONTH!!
Fortunately, I live where the maximum fine is only $1. BUT, if you don't pay up, before long, they send you a bill for the cost of the book. You are required to replace it for the library.
I've heard that in some locations, keeping library materials is "posession of stolen property" after a certain length of time. If you get pulled over for a speeding ticket, say, they can run your ID, find out about the library fine, and take you to jail for the overdue book!!
Good thing I don't speed, huh?