I've never really given much thought to the use of poison in
D&D 3.5/Pathfinder. Some monsters have it and can, on occasion, use it to good effect, but players rarely use it. First of all, there is the danger of a self-inflicted poisoning, a risk to which only assassins are immune. Also, poisons don't seem all that effective against any of the really powerful monsters you might actually want to use it on. Sure, you could use something like black lotus extract with its hefty save DC and its truly scary 1d6 Con damage per round, but at 4500 gp per dose, it isn't even remotely cost effective. Spells and swords can accomplish even more and generally don't cost a thing. However, with the addition of the alchemist class in Pathfinder, the use of poison is going to become more common and it may be time to examine the economics of poison (and alchemy in general).
I remember in the olden days, we used to butcher every poisonous monster we killed, trying to extract the precious poison glands for our own use or resale (assuming there wasn't a pesky paladin in the party). Of course, there was always a risk of being poisoned (an exaggerated risk, in my opinion), but it was worth it. There is, of course, nothing preventing a group from doing the same in
Pathfinder, but, depending on how firmly the DM adheres to treasure rules, adjustments would have to be made to include the value of any poison in the treasure of the encounter. This could get tricky since a monster may have multiple doses or it might use up all its available poison in the fight, so the value of its poison could vary wildly and may, in fact, be more valuable than any treasure such a monster might be expected to possess.
Next, there is the question of how to extract the poison. In older versions of D&D, it didn't matter, you just did it and hoped the DM didn't have a fight with his girlfriend the night before. These sorts of things are more formalized now, so some sort of skill check is called for. An appropriate knowledge skill might be a possibility, but that means a different skill for different types of monsters. Also, knowledge skills usually involve theoretical, rather than practical knowledge, like knowing where the wyvern's venom sac is located, but not necessarily how to extract it intact. Craft (alchemy) includes the ability to make poison, but doesn't really seem to imply the anatomical knowledge of poisonous creatures. Survival would seem to skirt along the edges of this activity, since it includes tracking and hunting. It wouldn't be a stretch to include butchering monsters for their valuable body parts and it is a class skill for alchemists, leading me to believe that is what the Pathfinder design team has in mind.
The upshot of all this is right now, poisons are way too expensive, even if you make your own, to be a significant part of any PCs bag of tricks. The alchemist class will likely require some rule changes to make poison use more accessible.
-Rognar-