At our local bonsai club meeting sometime back, a couple of guys had an interesting discussion on the merits of using charcoal as part of a bonsai soil mix. I can't remember what the outcome of the discussion was (probably more concerned about getting myself coffee and biccies, as usual) but this blogpost at Yamadori Passion may interest some of you:
Have a gander over there. Loads of great photos from his travels. My recent fave is his series of posts on the tools he uses for his yamadori. Good stuff.