Initiative helps determine who gores first in battle, and influences each 'round' of the fight (it you get hit, your opponent moves, or you otherwise are interrupted).
The prisoner just warns you about a trap, gives a hint on blocking the cogwheel in the arena (though it is better to fight the spiders, IMO) and a detect traps skill book (I never bothered learning that skill).
The DD and BD forums have been pretty quiet for awhile. There is sporadic activity, though (here and in the GOG Divinity forum and Steam discussion page for DD).
