Here's a nice gag for hanging an upside-down bookshelf on your wall -- the books are held in with elasticated strips of cloth:
/Inverted Bookshelf (via Neatorama)
The inverted bookshelf turns a bit of your living room upside down as it hangs all of the books from the bottom instead of supporting them from below. It's a satisfying optical trick and doesn't damage any of the books. In fact, you can take books in and out of it whenever you want.