Waterless composting toilet

Since we started planning our permaculture garden two years ago we have given most of our energy to water conservation, renewable energy, heirloom food gardening, worm generation, composting, indigenous planting, companion planting and buying less and less items packaged in plastic. But we haven't yet got to black and grey water recycling and composting. So, after talking with a friend yesterday, who has just returned from a NZ permaculture farm where he saw a basic, home-made one in successful operation, I decided it's time to build a composting worm toilet in the guest shed. Any tips or good advice most welcome.
Design from here.