I'm shopping for a rMBP and the 256GB flash thing is a big problem. I need OSX + Xcode for the occasional iOS app development, but mostly use Windows. OSX + Xcode and a few iOS emulator images is easily 100GB, so that leaves me with only 156GB on the Windows partition.
I don't mind paying for the higher end 512GB rMBP, but the discreet graphics is a deal-breaker for me. Thus I'm left with configuring the baseline integrated graphics rMBP with 512GB flash.