The problem with Permaculture is that it takes the classic "Anecdote is not data" misconception and turns it into a design philosophy. This can lead to some serious problems and you end up with a design philosophy that is completely divorced from the science.
For example, some of the key components of Permaculture Design - the use of nitrogen fixers and dynamic accumulators - stand on shaky ground. They're based on a limited number of studies. It's not clear whether dynamic accumulators actually add any nutrients to the soil. And for nitrogen fixers, it's not at all clear that the nitrogen they fix is available to the plants around them. It might not become available until they die back and rot.
This "personal observation" basis of the design philosophy that replaces careful experimentation leads to some pretty disasterous results - like Permaculturists being extremely laissez-faire about invasive species (which, after climate change and habitat loss is one of the top contributors to the loss of biodiversity world wide). I once heard a leading Permaculturist give this really fantastic lecture about the law of unintended consequences as it relates to human engineering, and then completely write off the risk of introducing invasive plants through novel ecosystem design. I mean, it's the same damned arrogance and mentality, just using plants in mimicry of nature instead of metal to dominate it.
So, personally, I've stopped encouraging people to listen to permaculturists. Permaculture is not the answer. Agroecology, however, the core kernel of Permaculture thought re-integrated with science, that holds _a lot_ of promise.