Ed:
I have been using DOs for about 6 years now, but only two to three times a year. I have two, a ten incher and a 12 incher. I also, on occassion use mountain pit irons, aka Jaffle irons to the down under crowd. The DOs I use have a rim on the lid to places coals there to aid in heating from top and bottom I use them mostly to bake, do stews and chiles. There are some DO sites and even an International Dutch Oven Society that I joined years ago..
http://www.idos.com/
International Dutch Oven Society
http://papadutch.home.comcast.net/
Byron's Dutch Oven Cooking Page
http://www.isu.edu/outdoor/dutch.html
II Dutch Oven Cooking Information and Recipes
The basic starting point for heat is to take the size of the oven, usually measured in its diamenter and subtract two coals to get the number of coals to start with under the DO. Add two coals to the diameter for the number to place on top. I know that this works well for my 10 and 12 inch ovens. To conserve fuel, usually charcoal brickets, you can stack smaller ovens on top of larger ovens. I have seen 3-5 ovens stacked this way. From that point adjust the number of coals as required to maintain the proper cooking temperature.