I stopped bothering with poison in PvE. Fights don't even last long enough for the 20% chance to come up. The weapon's enchant (seems to) trigger more often, for more damage, and all at once.
There are faster ways to kill than relying on poison to proc, at the expense of removing the weapon enchant.
As a nightblade, and I assume other classes are same, I can maim, reduce armor and DOT using my skills, all while weaving in light/heavy attacks that use the weapon enchant and build ultimate.
If I'm going to take my time, then I'm going to entertain myself seeing how many I can drag along on a kiting trip!