texan - you're conclusions are correct, but it's not technically the 'hardness' of the material that makes the difference in the plugs (no matter what marketing says...). What matters is the
melting point of the metal. Here are the melting points (in Celsius) of the common metals:
Copper == 1083
Steel == 1400-1500
Platinum == 1772
Iridium == 2410
The higher the melting point, the less electrode wear you'll get.
Someguy - copper plugs are great in high-compression, boosted, high-RPM, or any other high-heat engine. Because of the wide electrode, they do a great job at conducting heat away and preventing detonation causing hot-spots. But in a normal, cool street engine, platinum or iridium plugs (in a conventional configuration) should - in theory - provide a more reliable spark because of the sharper elecrode geometry; particularly at low-voltage and/or high-RPM conditions.
5_liter_eater - I'll just say I agree with texan and Someguy. Combustion chambers burn much hotter than 572 degrees F and can vary by thousands of degrees F between engine designs. Platinum plugs of the correct size and heat range will do absolutely no damage to a stock engine. And please take it easy on the cursing, this is a public forum.
Lots of basic info on spark plugs can be found in "Fritz's Treatise":
http://www.automotiveforums.com/vbul...threadid=13950