The only MMO I have ever played that had this feature was Ultima Online, and we used it all the time to make quests for players who wanted to join our guild, etc, etc.
In UO there may still be, to this day, books that I wrote when I played that game so many years ago. All that had to happen was that someone still owns the library that I put them in so they don't decay. This allows the player to leave a "leagcy" of their journey and new players can then read those books and find out what took place years ago in the MMO.
Please give us player writeable books, I am begging!