My third test involved suspending the “ideal” group of books so that it was no longer a pile on a surface, but a cluster in space. I found that because the books were all the same size it was not hard at all for them to remain stable. The formation was held up easily by nothing more than a shoelace, so weight is not as big of an issue as I had expected. Two important things happened:

a) By moving the books from the floor to a different height in space, the very nature of the space changed. While they actually took up a larger area, they were off of the floor (the most valuable real estate) and there was more room for me. 

b) The books became portable. I could easily move the group by holding a string, instead of carrying them with both of my arms. 

The importance of portability will obviously vary from user to user, but height will matter to all. A combination of the two would be useful across the board.