I'd like to expand on the topic of manuals. Manuals could be very useful. Say you have a Legendary Cheese Maker who also happens to be a Novice Writer. He could write a book about Cheese Making, and anybody who reads it would probably learn something. The better the writing skill, the better the resulting text. Same goes for the skill being written about, of course. I think, to make it not too over powered, a Legendary Cheese Maker (X)/Legendary Writer (Y) would make a manual that would give a Legendary Reader (Z) enough points to be a Competent Cheese Maker. That's three levels above Dabbling. Something like N= floor[(level of X)(level of Y)(level of Z)/3] could govern the amount of levels (from Dabbling) a dwarf could gain. So, from my example, if everybody is Legendary in everything (that is, X,Y and Z are all 15), N would be 3. Or something like that. Obviously we'd have to take traits into account as well. I think it'd be best if we just leave that part to Toady. I mean, he does have a PhD in Math and all. Another thing to consider: the Student skill.
Another thing manuals can be useful for: learning how to make foreign things. Let's say you want to make a turban. A dwarf would consult the relevant manual, and depending on his skill and the quality of the book, you'd get a turban. Such manuals could be obtained through caravans. Eventually, if the same dwarf reads from the same manual enough, he would eventually master the art of making turbans and it would be natural to him (and him alone). That means he doesn't need to consult the manual every time he needs to make a turban, and in fact could even make his own book about it, if need be.
Maybe we could expand this idea to include non-foreign items. Say you want to make a breastplate. If your Legendary Blacksmith authored a book on breastplate making (though why one would make a book on just one topic is a question for another day), then less experienced blacksmiths can consult that tome to make better breastplates. Eventually they'd be really good at it, and at Blacksmithing in general.
Just some things to consider. I really like the idea of learning from books; being the owner of a shit load of textbooks, I'd like to see my dwarfs know that feel.