Comfrey is a "must have" plant in the Forest Garden.
A couple of months ago, I wrote an article about Comfrey (Symphytum species). Literally the next day, this video was published by Paul Wheaton over at Permies.com. It is a great compilation of interviews of people speaking about this plant. Watch for Toby Hemenway, the author of Gaia's Garden - an excellent book on backyard permaculture.
Why permaculture folks love comfrey.