I bought my IS220d SE-L on 5th Jan.
I've covered just over 1000 miles and the fuel consumption average is 35mpg. Like most here I find 6th gear to be pretty much useless below 2000 rpm (85 ish).
My opinion, for what it's worth, is: Fuel consumption is ok for a brand new car. The gearing is too high for 6th. I've been using Esso fuel up until now, but I think I will try BP and see if there is a marked (or any) improvement.