I too would love this. I think it's important enough that, personally, I would have created a whole "diary" of sorts. Just a blank page where you can enter any text you want.
I often run one character at the office, and one at home, and I get confused what I have done with which. ..The idea of adding it to the quest-list screen is good. Might simplify the implementation.
Even if I wasn't running multiple characters, who has a good enough memory to recall their first kill on their 10th character for the week? Or, I've got pick-pockets now, dived the puppy cave, but have I killed Kranach? The puppy cave had the lawful alter on level three, and the Druid dungeon had the neutral altar on two .. or was it the other way around?
I vaguely remember the discussions of the past about it. But now that the resurrection campaign is under way, and we hope to bring ADOM to the masses, wouldn't it be more newbie-friendly to have things like note-taking integrated?
Of course, if this one of those "oh no, not again" topics, and there's no hope of it being considered, I apologise for beating an already well-beaten dead horse.