Most people buy paperback books because they don't want to pay twice or more for a hardcover edition. But I'll tell you something: once I went to my grandparents' home in the country and I found some shelves full of books, all of them at least thirty years old and some more than a century old. Hardcover books were nearly in perfect condition, ready to read again. Paperback books were crumbling to dust.
I know what most of you will say: "Yeah, well, that's right, but hardcover is still a robbery". Just think twice... Think that a book can last more than a life, and its value increases with time (not just monetary, but sentimental value). Paperback is good for books you won't really love and worship (Stephen King's crap, for example, and I know this can mean a few downvotes for me), but... you won't buy the Bible in paperback, would you? So please... when you're going to buy books, think about it: is it better buying two books in paperback, or just buying one in hardcover and asking a friend or a library for the other? Think about your grandchildren.