What is Biointensive Farming?

Tell me more about biointensive farming. I hear the term from time to time, and I want to know more. From what I gather, it's a way to grow a lot of food in a small space. Is it sustainable? What kind of people would benefit from this method the most? Where does it belong in the greater permaculture picture?

I've had a glance around the Grow Biointensive site. Very interesting stuff.

Anyone here have personal experience with this technique?