Will there be partial penetrations of armor? Like a spear piercing the breastplate but only scratching the skin? Or will it always either glance off or penetrate deeply?
Yeah, that'll happen. One of the quotes I collected
here discusses this: "The armor is all checked in order from outer to inner, then it gets at the tissue layers, altering the character of the attack as it goes." The attack probably loses energy (or something) as it penetrates.
Do we know if, say, "Dragon bone" will have different hardness / item value / shear strength or whatever than, say, "goblin bone" ? Would making dragon bone helms be worthwhile? What about Titan or Hydra bone?
The next version allows that kind of thing, but Toady's not saying which creatures have gotten special materials:
Speaking of unicorns what are the physical properties of theyr horn? Is it in some way extra pointy/sharp? What odd Monster-materials can we exspect?
It's going to be sort of lackluster at this point. There are lots of critters, and lots of materials that feel kind of magical have been left alone. There will be a few things.
Would leather from a hippo make tougher leather armor than leather from a cow? What about cave spider chitin?
Only if Toady set it up that way. I doubt he customized the properties of hippo leather -- might be hard to find data on that kind of thing. Chitin has a separate
material template, though, so we can see that chitin will generally be tougher against cuts than leather.
Is there a way to figure this kind of thing out from the raws?
Aside from the material templates above, and the few creature raws that have been posted, not really. Once we have our hands on the next version, then yeah, it'll be easy to tell from the raws which creatures have special materials.