Where things get really exciting is when you have an application that not only handles scaling properly, but also takes advantage of the added resolution. Take Aperture 3.3 for example. With OS X set to its “best for Retina display” mode, this is what Aperture looks like with a 2880 x 1800 image open and displayed at full size:
Here Apple is scaling the UI elements like the menus and widgets on the screen (backing scale factor = 2.0), but displaying the open image unscaled (backing scale factor = 1.0). As a result we can fit almost an entire 2880 x 1800 image on the screen without zooming out. Remember the backing scale factor isn’t global, individual elements on the screen can be scaled independently depending on their purpose.
The same thing happens when you look at applications like iMovie or Final Cut HD. The UI elements are scaled up but the video window is displayed unscaled, thus allowing us to display a full 1080p video alongside text and tools that are still legible.
It’s all handled amazingly well. It just works.