The book that you can write in takes up 20 spaces in the new sacks. That means you have to carry your books in the main slots of your inventory because it is not worth it to get a sack. I really should be able to carry some books in a sack. For most people this isn't a problem, but I'm trying to sell copies of my poetry book and trust me this is getting to be a problem. Also as a side note, mugs take up a lot of space too, making them hard to store.
