I'm pretty sure people have discussed this already but I was just thinking...
If the retina rumours are true, we're gonna have to deal with lots of blurry apps for some time, right?
If the screen is exactly 2x2 the resolution of the current iPad, then scaling would be perfect and non-retina apps would look just as sharp as they do on the current iPad. They'd look even better since you won't see the pixel structure of the screen.
The screen would have to be 2048x1536 resolution for that to be the case.