Well, I can help you with a few, but I've quit pumping bow skills for now. My archer/mage isn't finding 'em too useful. <img src="/ubbthreads/images/graemlins/winkwink.gif" alt="" /> Anyway...
Do the "bow" skills work with all arrow types, or just normal arrows? Does "piercing" simply increase piercing damage? Does it also apply to other arrow types?

I assume that the various "arrow proficiencies" get applied only if you're using the right kind of arrow?

Correct.

Most of the special arrows seem to do one special type of damage.

Correct, again.

Splitting arrows obviously split. Do you get more arrows with higher proficiency, or just more damage per arrow?

It looked like more damage, with the point I put into it.

Sorry I can't give you anymore help, Srikandi. I would if I could. <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />