Originally Posted by darthroush

Some are rated for 100,000 miles, but not all of them. Just because "platinum" is stamped on the package, doesn't mean you can toss them in and forget about them for 100K. OEM DoublePlatinum and OEM Iridium plugs can be rated for about that long though. Newer Toyota/Lexus vehicles use a Denso OEM Iridium plug that is rated for 120,000 miles. Regular, single platinum plugs don't fall into that category.

Here's some more about spark plug life. According to Autolite, you aren't supposed to use a regular copper core spark plug, or a "single" platinum spark plug in waste-spark ignition systems. What does Dodge use? A regular copper core plug. Denso recommends not running their Iridium plugs for more than 30,000 miles. Autolite and NGK say to change the plugs at the manufacturers recommendations.