"For those of you who like I have a 2006 GS300[or GS430], the proceedure in the manual to reset the oil maintenance light (p. 87) is either wrong, or at best poorly worded. To reset this light: 1. With the car running set the odometer to display total vehicle miles - not to the trip odometer. 2. Shut the vehicle off. 3. With the trip odometer reset button held down, switch the vehicle to on (ie push the start button twice without your foot on the brake)."
I found this on the Lexus Owners forum because I had the same question.