@Flobulon: I would love to train using books, but neither bulls nor male horses will give me anything to tan when butcherred, and the wild is a little too wild for a hunter to actually be able to survive.
Those giant bees are by far the worst wild things I encountered until now, even Aligators are at least limited to ground near rivers, those can also fly, and when a group exits the map, an other one (or the same?) seems to enter the map at most a season later.
Ah well, I guess 4 years is not so bad for a testing fort, I'll make more tests by butchering every animals I have to see who gives what.
Also, pet turtle lay eggs, but how long does it takes to actually make the babies come out? it's been nearly 2 years they laid, there is a male and two females, I locked the door, and even my hawks had the time to have two waves of kids.
Anyway, playing dwarf fortress is still fun (and FUN), even after all this time spent on it, that's amazing.
Edit, after reading your question, I experimented a bit before with books and libraries:
As noted in the documentation, the books won't always destroy, but I never could do much more than 3 or 4 per book, sometimes even only one, so I guess we are unlucky.
To add to the danger room topic, the documentation puts it in the tips and tricks, under "honorable mention", that is cruel of you to teach the new commers something that WILL get them FUN in a way they would not want while training, a little like when you equipped Steel weapons on training in old versions, where a champion would kill his sparring partners.