I was just rewatching the Teachings of don Jake and I finally realised what was going on, ie. the similarity to Castaneda's don Juan stories. The berry thing wasn't an accident at all - Jake fed everyone the berries deliberately to take them on a shamanic spiritual quest! Only Daria went and spoilt it by not eating hers, and then calling 911 just as they were getting really into their journey into another reality.
Jake & Helen had probably done this before when they were students, and decided to go on retreat again to seek spiritual renewal to overcome Jake's mid-life crisis / stress problems.
I thought the berries really brought out the best in Quinn, I think people like her benefit greatly from being dosed with hallucinogenic drugs (lets face it, she has nothing to lose). She might have a revelatory experience, and with a big enough dose her neural pathways might even get scrambled into something resembling intelligence.
It's kind of sad that Daria didn't take any, she might have turned into a great leader or something. I think we saw a rather straight-laced Daria in this episode, she might at least have sat out the trip and taken notes. She could have become the new Carlos Castaneda.
-Shez.