Hi...
For me, GLBasic shows 2048 x 1536 under iPad 3 (or "new" iPad...

)
I can't force in any way to show 1024 x 768 as a 2X application... it shows the app using retina resolution ever, just like the screenshots that Hark0 showed before. The image from games is showed in the top right corner (looking with the iPad in normal portrait) and the touch events are correct for the images...
Using SETSCREEN 1024, 768, 1 (or 0) appears to not have effect...
All my tests are done with Lion (10.7.3) and XCode 4.3.2
EDIT: I think that should exist a parameter that could be included in the info.plist of the XCode project to scale 1024x768 graphics up to 2X.