Even though the third-generation iPad is days away from announcement, and the probability of it containing a Retina display is merely a rumor at this point (although a credible one), iOS hacker/developer Ryan Petrich has taken it upon himself to tweak the iOS Simulator to simulate a Retina iPad display for testing purposes.
The whole point of this hack is to allow developers to test their iPad apps in 2x resolution in order for them to be optimized for the potential Retina third-generation iPad. That way, if the rumor turns out to be true (and we’re counting on it), those developers can have their apps optimized for the Retina display before everyone else.
The iOS Simulator hack is available from here, free of charge. In order to get it working, you’ll need to have OS X Lion and the latest version of Xcode available in the Mac App Store installed on your Mac.