Sorry - I haven't been online in a while and just saw your message.
I can't think of a "con", except that perhaps the Nav system will disappoint compared to the RL's. It is quite functional, but doesn't have some of the bells and whistles of the Acura system. In additon, it won't let you program while in motion (I got around that by buying an add-on device and installing it). Still, the Acura Nav system is the best in the industry by far.
Otherwise, you will find the LS460 to be powerful, quiet, roomy, comfortable, and economical - I get 18mpg or more in town, and often get 30mpg or more on the road. And that's with 380hp on tap! The nice features on the LS, like self-closing doors, extra seat adjustments, heated rear seats, etc., etc., are wonderful, and the Lexus service experience is top notch.
I haven't driven an AWD LS, but the owners on Club Lexus are thrilled. Excellent in snow and on dry roads.
I can't much of anything bad about the LS, since it's probably the finest car I've ever owned, and it's a joy to drive. Spend some time in one and see if you don't agree!
Mike
You wrote: "I'm thinking of replacing my RL with a 2009 Lexus LS460L AWD. What pros/cons to that idea (other than price)? Neuronbob suggested I PM you, since you have experience with both. Thanks for your help."