According to this tweet: https://twitter.com/#!/jury/status/180367953001324547
You have to compile and link with Xcode 4.3.1 against iOS SDK 5.1 in order to have the @2x retina versions of images loaded on the new iPad.
Has anyone actually verified this with real hardware?
Considering that Michael Jurewitz is an Apple evangelist, I would say that tweet is pretty authoritative.