In order to run it on the latest version of Xcode, you will need to symlink /Applications/Xcode.app/Contents/Developer to /Developer and /Developer4.
Meanwhile, stroughtonsmith shows how his app SameGame looks in the Retina iPad emulator running on his 27" iMac:
Click on image to see full size.
Apple is widely expected to release a Retina-enabled iPad 3 next week at their media event. If rumors are to believed, the iPad 3 should be available within a week or so of the announcement. That would leave developers little time to Retina-ize their current iPad apps if they wait until the day of the announcement.