Worth noting that not all these "fakes" are bad, or even inactive or less active. For example, most performers on the Burlesque scene have accounts specifically for their Burlesque personas, with names like "Kitty Cupcake" or "Tabitha Taboo" and the like. These are obviously not their real names, but a consequence of the fact that Burlesque performers don't want the offline attention on their personal or professional…
The problem there is that a person trying hard to keep personas separate can do so without Facebook being able to track (I assume they have to be more specific than just matching by IP address).