Hi Amit,
I too have a black IS200 and I had the Diamondbrite treatment. I was very pleased with the emd result. :)
As much as I tried all the other polishes and waxes such as Mer and Autoglym you could still see the swirl marks in it. Black seems to be particularly bad for that :(
However since the treatment, about 5 months ago, the car looks great after just a quick washdown and I haven't been using the conserver shampoo that you are supposed to either. :D
Gold membership discount should make it even better ;)