All of the replies stating that it would not add to gameplay are not giving the concept proper attention.
Consider this: you are ending your gaming session for the day and you will not be able to pick it up again for a week or so. You were in the middle of an unmarked puzzle and really needed to make a potion of night eye to get something in particular. The next clue in your puzzle is far away in another area, you've sort of figured it out, but aren't sure and you don't have the time left tonight to go get it. With an editable book, you can write in where you think the clue is pointing you toward and a reminder to get the ingredients for your potion. Without it, you pick up the game a week later (forgetting what you were doing) and only the marked quest is reminding you of your next task. Eventually in the next gaming session you remember that you were doing the unmarked quest but you've forgotten what your solution to the puzzle was and that you'd need a night eye potion.
The Elder Scrolls games are open world games in which the character can do a very large number of things. Because of this, the developers cannot foresee every single goal of a character, nor should they spend development time attempting to do so. It is an incredible waste of resources. So this leaves the an in game automatic journal entry system with a very simple quest oriented update system. Problems arise in a lack of updates for unmarked quests, personal notes and the like. (Marking every single quest causes the player to feel like his or her hand is being held throughout the game, leaving very little to feel special, secret or mysterious.) Suggesting that everyone playing should leave the game to use the internet, a third party word processor or a pencil and paper don't address the issue of having in game references.
A few gameplay advantageous uses:
- Having a hotkeyed list of ingredients helps a player not encumber themselves with useless ingredients.
- Having a recipe book of effective potions (especially mutli-effect potions) would have been helpful in past titles to eliminate trial and error for forgotten recipes.
- Writing reminders of cities or places in which transgressions occurred might help to keep the player out of prison.
- Writing reminders of places where strange looking objects were found can help players find certain objects when the need arises (if the player did not want to steal them initially).
- Writing reminders of enemy types associated with locations (necromancers in this dungeon, etc.) would help the player prepare for that location (bring resist shock equipment, etc.).
- Writing reminders of powerful enemies associated with locations (giant fish that I can't kill yet, etc.) would help the player remember where that enemy is when they eventually become more powerful.
- Writing the location of places in which you were unable to proceed (difficult locks, no key, etc.) and why not would help the player return later when that requirement was fulfilled.
- Writing a list of names of the people you have murdered in case later quests, found notes or the like refer to these individuals.
- Writing unmarked locations down in direction form (east from Fort Erehwon before Camp Erehwemos).
- Writing your intent to kill an NPC who particularly pisses you off but you haven't been able to run into them alone just yet.
Some may say that the last few in the list are not actually gameplay, but I challenge that they are. Because the game is open world and there are a virtually infinite number of things to do (most players will not even do half of the possibilities if the previous games are any indication) emergent gameplay becomes part of the gameplay and charm of the game. While this may mean attempting to cheat the magic or alchemy system it may also mean attempting to fine tune play within the existing systems (magic, alchemy, barter, stealth, social). Having notes handy would help most players. Again, most players will not use half of the resources available to them in this game. So, just because it's not being used should it be there? I'd answer yes. Otherwise, we'd all be playing a Nord Warrior on a very linear quest.
Simply, there is much advantage to having an in game reference that updates things such as in game time rather than running in between the computer and the game while doing so (for console players) or opening up the game and closing it (for PC players before this mod will obviously be made) or writing it all down on scrap pieces of paper that become lost or forgotten or a notebook. What I find far more ridiculous than the suggestion of editable stationary for the game is the overabundance of blank parchment, quills and inkwells in Oblivion. It's almost as if editable reading material was planned and then left out. For crying out loud, in Skyrim we are going to be able to far more boring activities such as cuting wood and mining, why can't we do something like write notes about our gameplay? It is not difficult to create such a thing (as it has been done for the past two TES games by modders).
Since this is mostly a request for console users (as it would likely be made as a mod for PC play) the argument that the virtual keyboard is awkward doesn't hold water. I've used it throughout Oblivion to take notes by creating potions and naming them what note I was going to make. This becomes heavy, however, and is only a workaround for a lacking feature in the game.
CONCLUSION: If you don't like writing or reading, that's fine. You don't have to do that, just like you don't have to be a mage or a thief if you don't want to. However, there is an option to be a mage or a thief in game, just as there is an option to read books. What we are asking for is the option to write, as well, because we like doing that, we know it can be useful and we know it can be done. You don't have to like it, just like you don't have to like using skooma.