Our son Jon and his wife Anna began a keyhole garden some two years ago, note the angle of teh bricks, the photo is just a segment of this vast permaculture process. I have done raised garden beds, but not in this style. The graphic below (from: davesgarden.com) explains the simplicity and theory well in visual form
This photo (api.ning.com) shows what it looks like early on, this one is laid with bricks flat. People have made them out of metal sheeting, plastic liners, cardboard, etc. In this photo you can see the central compost tower which receives your scraps daily and which feeds the garden daily. The raised bed is moisture retaining and ergonomic in that it is ideal for waist height gardening. It is drought resistant too, and water wise. It is a no dig garden, and permaculture is the theory behind it. It works well by every testimony online, and Jon has said before it has worked well for them. What a great theory!