Apparently, Amazon holds a 40% stake in Abebooks which owns LibraryThing. From Pandodaily, "Amazon already owns Shelfari as well as Abebooks, which bought a 40-percent stake in LibraryThing in 2006, so it owns all or part of three of the top social-reading sites."

http://pandodaily.com/2013/03/28/amazon-bought-goodreads-but...