From Book Crossing, a testimony:

Take BookCrossing.com. On the face of it, it presents no profound challenge to established publishing practices and to the modern concept of intellectual property. Members register their books, obtain a BCID (BookCrossing ID Number) and then give the book to someone, or simply leave it lying around for a total stranger to find. Henceforth, fate determines the chain of events. Eventual successive owners of the volume are supposed to report to BookCrossing (by e-mail) about the books and their whereabouts, thereby generating moving plots and mapping the territory of literacy and bibliomania. This innocuous model subversively undermines the concept - legal and moral - of ownership. It also expropriates the book from the realm of passive, inert objects and transforms it into a catalyst of human interactions across time and space. In other words, it returns the book to its origins: a time capsule, a time machine and the embodiment of a historical narrative.

by Sam Vaknin - who's working in a surprising, but interesting field - that of narcissism.