I finally decided to play around with Minecraft's trading system, and wanted to get some diamond tools. So I made a bunch of written books, and went to find a Librarian to trade with. He wouldn't take them. The only offer he had was for regular books (or maybe paper, I forget). Back to the crafting table. Eventually, he changed up his offers to the point where he would trade me written books for emeralds - I had my first emerald!
That went on half a dozen or so time, until apparently he'd had his fill of books, and no new offer types appeared.
Which got me to wondering, is trading worth it? For non-enchanted items like diamond tools, would it be faster just to mine for diamonds, than trying to get all the little things needed to trade, hoping you can trade them, and the person doesn't get tired of them...