It was something that popped in my head when posting on a subject.
But what if to learn certain things like crafts/spells (obvious for some) there were hidden books/scrolls/wall glyphs that would teach you how to do it. These books would have a long respawn rate or none thus putting a sort of market on them; if someone would, for a price, teach another what he learned. That person could teach someone else, but only after they themselves put the that knowledge to work and actually craft the item/spell first (that way you just can't learn it to teach a friend, if you didn't have the skill to begin with). This last part goes with if they don't want to share the book to chance losing it, or the person they are teaching wouldn't have the means to read the material.
This would also be something to have if knowledge skills play a part to know how to fight a monster; where you can give a bonus to your party when they encounter said monster. "I know that this school of magic will not work against this monster." Bards rejoice!
I can see problems with this as well, people fighting for it or the more hard core players gathering them all first; but that's part of the adventure and can't say a hard core player will hit everywhere.
Also say even having the book you still have to decipher and learn from it, so that takes time. You have to put the effort into it learning the material so it's not an easy effort for some books to learn what they hold if you can't get around maybe magic enchantments or the language the words are in. (Another adventure or quest to complete)
It's just a thought... and now it's out of my head wheeee
