In our teenage years, a friend and I used black powder to blow a stump in his backyard. We had been digging for hours, and decided to use a more, umm, "expedient" method of removal. We decided that about a pound of FFG ought to do the trick, and it did, to the effect of a stump going about 20 feet higher than the roof of his parents 2 story home.
WE thought it was really neat, if loud. His parents, neighbors, and the local police dept did not agree with us, except the loud part. Many lectures ensued <img src="images/graemlins/frown.gif" alt="" />
So, lesson learned, don't use black powder to blow stumps.
Rob, I think there is a bacterial based product that causes the stumps to rot very rapidly. Ace Hardware carried it before, someone may have it in your area.