Via Gruber, interesting discussion
of when we can reasonably expect Retina level displays at iPad sizes in the context of Moore's Law.
We want to achieve 1024x768 times two = 2048x1536 = (2.13*960)x(2.40*640) = about 5x the physical area of the iPhone 4.
Moore's law says we get 2x every 18 months. So 5x is 2**2.32, ie. 2.32 doubling periods, or 3.48 years.
By that calculation, we can expect to see a double-resolution iPad 3.48 years from its original release date in March 2010, ie. Christmas 2013. (We can expect that Apple will have secret test units long before that, as they would have with the iPhone 4, but that doesn't change anything since they do it consistently. We can also assume that if you're willing to pay zillions of dollars, you could have a large display like that - produced by lucky fluke in an error-prone process - much sooner. And of course you'll get almost-as-good-but-not-retina very-high-res Android tablets sooner than that.)
Note: all of the above assumes that Apple will choose to define "retina display" as the same DPI for the iPad as for the iPhone. They probably won't. Being masters of reality distortion, I would bet on them being able to deliver their newly-redefined "retina display" iPads at least a year sooner at a lower DPI. So let's say sometime in 2012 instead. But not 2011.
The 2012 date assumes Apple would be willing to accept some intermediate, scaling requiring res for a "Retina" iPad, but I'm not so sure. As the same guy points out earlier in his post, it was pretty smart for Apple to wait till they could double the original iPhone's resolution, even as the competition kept releasing incremental increases. Doing the same thing with the iPad would be smart, even though it would mean standing pat while Android tablets trumpet their "better screens."
OTOH, as I've posted elsewhere, the next year is a pretty critical time for the iPad, and Apple may be willing to change it up a bit just to keep Android from getting a foot in the door.