I only just noticed this today when I was editing some pictures in Photoshop using Windows (Boot Camp). My version is Windows 8 64-bit and the Photoshop is CS 6 but I suspect the same thing would happen even if I were using Windows 7.
Whenever I view an image in Firefox, Chrome, Windows Picture Viewer or any other program besides Photoshop, the image is always displayed as it is and appears as crisp and sharp as it should. For example, if I load a picture that's 600x600 pixels outside of Photoshop, it would look exactly like it is - at 600x600.
But once I open it in Photoshop, and if it happens to be a very big picture (which it is for me, most of the time), the picture would look resized (i.e. smaller), but the Photoshop navigator would still say it's displayed at 100% magnification. So a 2000x2000 picture would basically look half its real size but still be at a zoom setting of 100% according to Photoshop.
That in itself isn't the problem, but trying to edit/crop the image is. If I were to select a part of the picture and resize it to, say, 100x100 pixels, the final image would be a bit blurry, even if I save it at "most high" quality. That obviously makes my image "un-usable" because the quality is so terrible. This doesn't happen at all on a computer without retina display but on mine it makes the task of editing images in Photoshop frustrating and pointless.
I really think it's an issue with retina display's native resolution not being supported in any version of Windows, so I'm hoping anyone who uses a Macbook Pro RD, Windows AND Photoshop could help me get around this problem.