Re thermometer, Derek, you've gotta stop giving away these secret tips, I need every edge I can get. I also use a digital timer, many might say an unnecessary extra but as a senior citizen I find it saves that, "Did I put that on at 10 to or 10 past ?" They are also at K Mart for about $4.95.
Rob

http://papadutch.home.comcast.net/LodgeBakingTempChart.doc This is the temp. chart I use and works very well.      
Generally speaking each briquette will produce about 10° - 15° F. worth of heat on a moderately warm day with no wind. However, do not use these numbers to try and formulate how many briquettes you should use to generate internal oven temperatures. Instead, use the general rule of thumb to calculate the number of briquettes to reach 350° F. and then add or subtract briquettes to reach the temperature you desire. Why shouldn't you use the heat values to determine temperature? The answer is, other factors such as the amount of metal used to manufacture the oven, the size of the oven (volume), and the amount of free airspace inside the oven affect the final internal temperature the oven will reach when using a set number of briquettes. The more metal, volume of food, and internal air space you have to heat up, the more heat will be required to bring your oven to the desired temperature.

Other factors such as ambient air temperature, humidity, altitude, and wind all influence how much heat is generated by burning briquettes. Cool air temperatures, high altitudes, shade, and high humidity will decrease the amount of heat generated by briquettes. Hot air temperatures, low altitude, direct sunlight, and wind will increase the amount of heat generated by briquettes. Also note that in windy conditions briquettes will burn faster due to the increased air flow around them, so they will not last as long.

Heat placement around the Dutch oven is crucial to yield the best cooking results. Briquettes placed under the oven should be arranged in a circular pattern no less than 1/2" from the outside edge of the oven. Briquettes placed on the lid should be spread out in a checkerboard pattern. Try to avoid bunching the briquettes as this causes hot spots.

The number one question I am asked is "How many briquettes should I put on the lid and how many should go underneath the oven?". The answer is "It depends on what you are cooking".

For food you wish to simmer such as soups, stews, and chili's; place 1/3 of the total briquettes on the lid and 2/3 under the oven.

For food you wish to bake such as breads and rolls, biscuits, cakes, pies and cobblers (rising); place 2/3 of the total briquettes on the lid and 1/3 underneath the oven.

For food you wish to roast such as meats, poultry, casseroles, quiche, vegetables, and cobblers (non-rising); use an even distribution of briquettes on the lid and underneath the oven.

The golden rule of Dutch oven cooking is "go easy with the heat". If the oven isn't hot enough you can always add more briquettes, but once food is burned, it's burned.

This is the web site for the info on where to put the charcoal briquets(heat beads) http://papadutch.home.comcast.net

Bobkat, your a bloody legend. Thanks for that little chart, it's a beauty. 
Regards,
Ned