This almost certainly exaggerates the actual cannibalization of book sales by libraries (consumer marketers know that self reported purchase intent notoriously overstates actual purchasebehavior), but cannibalization does occur.
Although Facebook has the user base and Web-based engagement that most social companies dream of, the network is lacking the type of consumerbehavior that is easily monetized in later cycles of purchase intent.
Tracking in store purchasebehavior will also enable brands with deeper insight of consumer preferences, augment social profiles and build more personal relationships.