Interesting thread. I'm about to become an IS250 owner and it will be interesting to see how my brakes last. I see EBC do replacement discs for the IS now.
I've just replaced all the pads on my wife's Subaru Tribeca. The dealer said they all had only 1,000 miles left in them; the fronts were low but the rears were less than half worn........at 40,000miles! The fronts on my previous Impreza were generally lasting about 35k miles and the rears 65k. I know the IS is pretty heavy for its size but it does sound like the parts are marginal - unless you spend your life on the motorway.