You have to look extremely hard to find any fault with the '06 Lexus IS 350 sedan. I bought one last weekend with the sport package and the Mark Levinson/navigation package and I feel like I'm 16 again and just got my driver's license. Not only is it a FAR superior car to the boring BMW 3- series, it's quite a drastic change from the old IS series. Handling and acceleration are superb and driving enjoyment could not be greater. I actually prefer this car to the Porsche 911 (2005 model) I was driving now and then prior to this. Way to go, Lexus...amazing job.
Navigation system/guidance, ability to play DVD videos (while stopped only, thank god), handling, headlights that turn with the car, fantastic exhaust note when you slam the pedal down hard, Tiptronic transmission is excellent, too, with paddle shifting making things even more fun.
A bit more user-friendly mapping system...hard to delete previous destinations/points of interest without really reading the manual in detail. Other than that, car is almost flawless.