When Apple announced the Retina display MacBook Pro, one of the applications which they demonstrated with it was Photoshop. But not a release version of Photoshop. The current release version of CS6 opens images at the same size, and the same resolution, as on a non-Retina display MBP. In comparison, Apple’s own Preview app opens images at half the width and height as 100% view, and displays all the pixels in the image at that size. For comparison here is an image at 100% view in Preview on the right, and viewed at the same size in Photoshop CS6 on the left. If you look at the narrow yellow leaf stems at the focal center of the image (left of center in the crops shown here), you can see the difference; be sure to click on the image to see at full size.
I expect that the Retina display update to Photoshop will be free… for CS6 owners. But it is unlikely that Adobe will update Photoshop 5 to Retina resolution, as one more reason for users to update to CS6.
Be sure to check out my articles on the Retina display MacBook Pro’s screen, reflectivity, and color gamut, as I publish them over the next day or two.