When SPIN first came out, I bought the PDFs. Basically they teach you how to get a lot of yield out of a small space by growing things in succession and growing varieties that produce in relatively short time frame (so you can get successive crops). They also show you how, if you lack
land of your own, you can approach neighbors or landholders and essentially farm their properties.
It's interesting information and something that Stacey Murphy is doing as well. Is it
permaculture? Not specifically - but it could be made to be more "permaculturish" with the addition of
water harvesting elements,
trees, nitrogen fixing plants, pollinator forage areas, etc.
For me, the information was interesting but not all that useful due to my climate. We tend not to use raised beds in the desert due to the fact that they waste precious water. Also, it takes on average about 3 years for us to build decent "veggie garden" soil. While I've spent the time to set up water harvesting, sunken beds and soil building on my own property, it's a lot of work. I doubt that I would want to invest all that effort on someone else's property for very little yield for several years. Plus, I grow stuff under the shade of trees - which need to mature. Otherwise I need shade cloth during certain seasons. I will also always need to rely on some form of irrigation during most of the year.