Just an explanation, for those who don't know; this is how it "should" work according to PnP.
1. Applying any contact type poison to a blade always incurs a 5% chance of self-poisoning. This is the risk which the "poison use" feat eliminates. Although this is nice, as you can see, it is not "huge" unless you are using poisons which alone can kill you. (And those would be extremely rare and powerful.)
2. Rolling a 1 in combat means your unlucky self fumbles, and you may poison yourself with the weapon. This is where you normally roll a DC 15 reflex save in PnP to see if you can avoid being poisoned.
3. Buying poison or having it on yourself is typically illegal.
4. Traps can include contact poisons, and as such you would assume that they last longer than 3 or 4 rounds after application. Although I'm not sure of any "official" rule, I think a fair DM would agree that the timer should not start running until you start using the poisoned weapon in combat, at the very least; perhaps from the time you first use the weapon against something until an hour or so IG.
(If you wanted to be picky, you could also determine how many "hits" the weapon could do before the poison is all cleaned off from the weapon once you start hitting stuff. Of course, cheaper versions of the poison being weak and dispersing fast, and more expensive versions of the same substance sticking to the blade for a longer time.)
It seems NWN once again half-arsed their implementation. As you can see, classes that gain higher reflexes are supposed to get substantially better at not accidentally poisoning themselves when it really matters, which is in combat. (NWN's absurdly low poison duration means that even the poison application itself must by default practically be in combat anyway, though.) Losing the 5% chance when prepping a weapon is nice, but not so much of a big deal while you're not using high-powered stuff.
(I kind of suspect that they grabbed the DCs that are meant for the combat reflex saves, and shoe-horned dex checks in for it instead, god knows why. Maybe the lack of "moral repercussions" in the OC made them decide it was better to make them much more difficult to use, or perhaps it was because there was no longer any real risk of poisoning yourself during combat.)
Edit: Ok, so this is in suggestions, I guess I better suggest something. Here we go...
1. Make poisons last longer.
2. Make them slightly easier to use, or switch back to a reflex-save application.
3. Add a chance of carrying "poison sacs" to any creature with natural venom.
4. Remove all poisons from vendors. Instead, replace these with some sort of venom-processing device, ("Small fluid distiller?") which you can operate to make a usable poison from aforementioned poison sacs.
5. Possibly have some "harvestable" poison types in the wilds as well, for making ingestable poisons.