Gentlemen, I might be barking up the wrong tree here, from all your comments it sounds like you are all suffering from what is known as 'Flares', when you De-cell and disengage the clutch your engine speed increases maybe by a couple of hundred RPM, this is trade-off with 'Tip In/ Tip out' the more the 'Dash pot' is reduced 'Engine cal term' for engine brakeing. the less 'Engine Brake' you have and the better tip in (bump)and tip out (bump), this would be more annoying than the 'flares' as these cause a low frequency oscillations which can cause car sickness for passengers during city driving.
Although I don't own an IS200, Currenlty car is on order (see below) when I had a test drive of a IS200 SE, I didn't notice any flares on the gear change, The only thing I had an issue with was the 'Fly by Wire' throttle, it took a while to get used to, it seemed a little to sensitive to me, that said, try and change your driving style a little. When you accellerate step in a little further and for slightly longer before changing gear, a little difficult with 1st as I found it a little to short. Lexus might have made a better job of the transmission if they had picked a ratio between 1st and 2nd for 1st gear and then only had a 5 speed transmission which may have been better for Drivability but not for marketing. The last thing I will say is, When I finally get my hands on mine and if it suffers from 'Flares' I will be straight back to the dealer complaining