I once read part of a book on recreational mathematics that told a variety of stories. A central part of each story was a piece of non-trivial, and very interesting mathematics: the sofa moving problem, and finite projective planes are two topics that I am sure it covered.
My question: what is the title of this book?
Well here's a guess: Another Fine Math You've Gotten Me Into, by Ian Stewart.
http://books.google.com/books?id=ZfK7AQAAQBAJ&printsec=frontcover&vq=Sofa&output=html_text&source=gbs_ge_summary_r&cad=0