I just took delivery of my "Liquid Platinum" GS350 and I am loving it. I have gotten a few thumbs up, and lots of "how do you like it?".
We had recently purchased a M37 as well, so my wife and I are really able to compare the sporty versions of Japans luxury contestants. The Lexus retains a sporty presence without a harsh ride, and the six speed transmission delivers right-now power. The engine reminds me of a sport bike audible note, while the M37 has more of a Harley growl.
The Infotainment system is exceptional. The 12.3" screen for the navigation and basically all other functions takes some getting used too. The manual is as thick as an encyclopedia, which can be overwhelming if you are not a techie. Once I played with the system for a few days, the "mouse" like device became easier to use, and there is an option to increase feedback that you get from the mouse. I have not found a need to use the hard keys for the radio, and AC since everything can be done through the infotainment system.
The overall cabin feel is a little bit tighter than the M37. The M37 feels like a much heavier car than the Lexus, but the Lexus offers a much smoother powertrain. Lexus missed the opportunity to increase the power to match the German competitors and even it's Japanese counterpart. The infotainment system has too many functions, if that is possible.