I agree with getting rid of grease and grenade for poison thieves. I must have greased a dozen weapons, and they never dropped them once. Give them a damaging poison type instead of grenade, something that lasts a long time and can be used in ranking! Or doesn't last long but doesn't require ingredients. Also nick should definately be lowered or the amount a poisoned weapon acutally poisons raised. I remember rarely hitting with my poisoned weapons.

If they tweaked poison thieves just abit more to make them more player friendly, I'd try them again.

Down with grease and grenade!
Up with damaging poison!

That which does not kill us,
makes us stronger.