Hi Rick, I wondered the same thing. What does a 1920x1080 72dpi Photoshop document look on the retina display? I went to an Apple Store and played around and the answer is that in Photoshop, the physical size of the document at 100% is the same on the 2880x1800 Retina Display as it is on the 1440x900 legacy 15" MacBook Pro. But the content within that document is jaggy and pixelated as if you were viewing it at 200%.
For some silly reason, the Apple Store employees hadn't bothered to install the Aperture and Final Cut Pro X software updates that grant those Apps retina display support, so I wasn't able to see this 1080p video at 100% they were raving about at WWDC, and photos in Aperture looked blurry.
It seems that for content creators building 72dpi screen images for video and web, the retina display is going to be a hindrance as all of your content will look low res when viewed at 100%. I guess my question is how will this change when Photoshop and other Adobe apps get updated for retina display? Will a 1920x1080 72dpi document at 100% take up half as much screen space as it does now, so that you're viewing it pixel for pixel? This to me would seem like the ideal situation; then if I were designing a 728x90 web banner I could build it at 1,456x180, then just save it out at half-size when finished.