being that lexus' are made by toyota and anything that toyota makes you can bet on... just like honda/acura... but with a little more class...
while it is a new car, the engine is not new, and toyota knows how to do awd, this has been proven on MANY previous models... i wouldn't worry one bit... they are also some of the best backed cars in the industry... even if they don't just "give away" their 100,000mi/10yr warranties like other car companies do just to "get you in the door," so to speak... enjoy your new ride!
_benjammin