So since 1.4 I've had this idea in one of my single player worlds. 1.5 made it possible to make a compact vertical block swapper(?) using redstone blocks. It is a variable enchanting room that allows you to have anywhere from 0 to 15 bookshelves around the enchanting table. I haven't seen any enchanting rooms that let you pick any number of books, but there might be one out there somewhere. When you press the button it will add a bookshelf. If you push it when all the bookshelves are showing, they will all swap back to stone brick.

If you want an explanation of how it works, watch the video below. If you have any questions feel free to ask them.

Leaving a like here is much appreciated. :)