How to accommodate for the iPhone 4 screen resolution?

According to Supporting High-Resolution Screens In Views, from the Apple docs:

On devices with high-resolution screens, the imageNamed:, imageWithContentsOfFile:, and initWithContentsOfFile: methods automatically looks for a version of the requested image with the @2x modifier in its name. It if finds one, it loads that image instead. If you do not provide a high-resolution version of a given image, the image object still loads a standard-resolution image (if one exists) and scales it during drawing.

When it loads an image, a UIImage object automatically sets the size and scale properties to appropriate values based on the suffix of the image file. For standard resolution images, it sets the scale property to 1.0 and sets the size of the image to the image’s pixel dimensions. For images with the @2x suffix in the filename, it sets the scale property to 2.0 and halves the width and height values to compensate for the scale factor. These halved values correlate correctly to the point-based dimensions you need to use in the logical coordinate space to render the image.

This is purely speculation, but if the resolution really is 960 x 640 - that's exactly twice as high a resolution as the current version. It would be trivially simple for the iPhone to check the apps build target and detect a legacy version of the app and simply scale it by 2. You'd never notice the difference.

Engadget's reporting of the keynote included the following transcript from Steve Jobs

...It makes it so your apps run automatically on this, but it renders your text and controls in the higher resolution. Your apps look even better, but if you do a little bit of work, then they will look stunning. So we suggest that you do that

So I infer from that, if you use existing APIs your app will get scaled up. If you take advantage of new iOS4 APIs, you can get all groovy with the new pixels.