Well from my understanding of it
Poison weapons have there own poison values the upper end which is actually the under used snake sword (being the most poisonous weapon of all of them). The actual skill poisoning last i heard does nothing or next to nothing and really does not need to be trained. The delivery of poison to an enemy is by proc(action; in this case the proc happens via attacking) which is also controlled by the weapons values, along with other factors such as the number of accurate hits you make (more hits you land the more chances to poison)
Magic poison (YEG KEL) can stack to a certain degree
Weapon poison does not stack seem to stack
In head to head combat there are no or very little difference between a poisoned weapon and it's normal counterpart in most cases. for example a poisoned ornate dagger is just as damaging as an ornate dagger, but the former has the chance to poison you.
Poison damage does not seem to have any effect on monsters.
Killing with poison is relative to HP. high constitution characters hardly feel poison effects from the lesser level of poison (yes it comes in levels). I've seen characters with 16-20 con survive spider bites by doing nothing more then sitting still and keeping there character fed until it passed.
Poison works best against low constitution enemies. If you disengage from combat it gives them a chance to get rid of the poison. mage's for example will cure there poison using magic and warriors can drink a potion. You won't often find that poison kills the prepared person on it's own.
Perhaps if a GM or Dev happens by they can tell us what the poisoning levels are by name, and do the usual confirm or deny.