I haven't used LibraryThing because I know if I started I would become obsessive and not stop, which means I'd spend all my waking hours cataloguing my books. So I never knew about some of the fun to be had with LibraryThing until I saw this great linkdump from Free Range Librarian with a link to ... are you ready......
I SEE DEAD PEOPLE['S BOOKS]
which is a group pulling together information on the personal libraries (some in progress, some complete) of various famous dead people. For instance: James Joyce, Karen Blixen, Danilo Kis, Sylvia Plath, Walker Percy, Ezra Pound, Robert E. Howard, and Tupac Shakur.
Alas, no Borges. Yet.