I say that there should be added so called "skill books" aswell...
From these books player will be able lear(obviously) skills to make these books you will require 2 skills, mentoring and skill you want to write about. It should work basically the same as mentoring but simply quicker. I suggest you should req 100 in mentoring and other skill and hard to acquire materials, howether i know that it would be little game breaking so i would suggest aswell to make other restriction to make these books very very rare. Hell after all books in the middle ages were very rare...
Just my little addition to books in game...
I am ashamed of myself for stealing attention sorry ...