"Orphan Works" probably comprise the majority of the record of 20th century culture. These works are still presumably under copyright (only works published before 1923 are conclusively in the public domain), but the copyright owner cannot be found. The default response of archivists, libraries, film restorers, artists, scholars, educators, publishers, and others is to drop copyrighted work unless it is clearly in the public domain. As a result, orphan works are not used in new creative efforts or made available to the public due to uncertainty over their copyright status, even when there is no longer anyone claiming copyright ownership, or the owner no longer has any objection to such use.Link (Thanks, Jamie!)
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.