I seem to be collecting both paper and e-books. I tend to get woodworking, history, books that I will continue to reference and things that I find historically interesting in paper form. Things I am likely to read once I try to check out from the library, and non-fiction I want to keep will be in whatever form I find them. In our house we have more than 10k paper books, and probably 3-4k of e-books. I dread having to move.