My husband grew up in a family that buys books (and went to the library); I grew up in a family that only went to the library. It drives me nuts when he buys a book that he could just borrow from the library. For a while we had a deal that for every new item of clothing I bought, he was allowed to buy a book. He has acquired a large Steven King collection, which drives me even more nuts because they are books that I don't like to read! Since half of our house is under construction and we never had a lot of bookshelves to begin with, we have had piles of his books just sitting in bags in the spare bedroom. When he finished installing the ducts for the new heating system in there on Sunday, there was dust EVERYWHERE, so I had to do some major cleaning. I decided that we needed to put these books somewhere, but buying a bookshelf isn't at the top of the list right now and my brother is already building my daughter a closet so I can't ask him to make me one.
My husband used to keep several hives of bees and so we have lots of equipment in the shed. I thought that the empty super cases would make good simple bookcases. So I got him to pull out the cleanest two for me and I washed them off. Not the prettiest, but totally simple, free, and easy to take apart when we eventually get a real bookshelf.