Originally Posted by rrounds

One thing about the gap. If it's just a Iridium plug, with a standard ground electrode, the gap will increase as the ground electrode wears out. If it has a platinum ground electrode(with a Iridium or Platinum center electrode) the gap should stay the same even with 200k miles. I've seen this first hand, but just because the gap is the same doesn't mean the rest of the plug is still working like it should.
That said I have never had a Iridium plug go bad in 100k mile change intervals.

Rod