The under-stair case looks really nifty and I like the visual aesthetics of the two round ones and the surrealist-looking left-hand on the bottom and 9th down in the centre column ones, although I question their practicality in easily allowing access to the books to be read.
Apparently not included, but also nifty: the modular Tetris bookcase, for which you can find
DIY instructions or apparently buy
pre-made components commercially (
more action pics which seem to be made from those). Here's
another variant which can be rearranged in neat formations, and here someone's
combined the bookcase with foldout bed storage.
And via neatorama, the
bathtub made of old books, which is apparently intended to eventually be functional.
ETA: Apparently that circular bookcase in the OP link is
supposed to function like a hamster wheel, in theory at least.