My Lexus just turned over 283k miles. Had the spark plugs changed here is what was pulled out:
Unsure when they were last changed (nothing mentioned in the 30 pages of service documents). Car runs better, but nothing "felt" wrong with it before. Just doing routine stuff in the mean time. Idle has been perfect since day one (drove it from dealer in Palatine, IL) and past few months. I would say this is a testament to Toyota quality.
edit: Changed with NGK plugs.