So... three years later and my trusty IS200 Sport has been swapped for a GS450h SE-L. Wise move? Only time will tell :)
I've only had the car for about two days, but everything that I've read about it appears to be true so far; it's fast, smooth, and very relaxing to drive. The brisk acceleration from any speed is certainly its party piece, and watching the hybrid system in action is very interesting. Average consumption has been 35 mpg (according to the computer). A totally different animal to the IS200 then, to put it another way.
That said, I do feel that the GS450h lacks the overall solidness of the IS200. What used to be a reassuring "thud" in the IS (when shutting the boot, closing the doors, etc) feels more like a "clunk" in the GS. And its interior certainly creaks a lot more than the IS.
Now for some pics:
I also just realised one more thing: the IS200 had a silver exterior with a black interior, which made it easier to keep it looking spotless for longer. The GS450h on the other hand has a dark exterior with a bright interior... happy days :P