Funny, I was just in a conversation with a coworker on the merits of copper, iridium, and platinum plugs. It's good to see information from someone in a position to know.
Jay Buckley is the Technical Manager (which means he teaches mechanics around the world) for Honeywell Consumer Products (Autolite, Fram, Prestone), is an ASE and Michigan Master Technician (30 yrs), and (part?) owner of Motorking Automotive (22yrs?) in Shelby Twp, Michigan. I like the hell out of where this information is coming from.