Just put a set of Denso Iridium IK16R11's in about a week ago. Difficult to tell if it was an improvement over standard as my last set of plugs were the wrong ones (Camry plugs) put in by a Toyota dealer 50,000 miles ago and were causing a misfire.
Got mine from www.sparkplugs.co.uk next day which was quick, they are cheapest from ebay but delivery was a lot longer when i looked.