I just tested my app with the new ipad (iPad 3). It is running with the UIDeviceFamily 2. So you do not have to change anything at the moment.
The Resolution of the app is than 160 dpi and not 240 dpi as expected.
Also, if i set the requestedDisplayResolution to high does not change anything. I am searching for a solution...
My understanding is that if you design to the lowest DPI, you can have it automatically scale for higher DPI settings.
There are two important properties of the application:
It is recommended to set the applicationDPI to 160 dpi (the lowest DPI that you want to provide, 160 DPI is the used for iPhone 3Gs and iPad 1 + 2).
With these settings your layout looks good on all devices.
Fonts and vector graphics are scaled up to the right size (e.g. you have a vector graphic that is 10 px height, than this graphic on a device with 320 DPI the graphic is 20 px, but you don't have to care about that).
Flex uses categories at 160 DPI, 240 DPI or 320 DPI. If your device has let's say 266 DPI (iPad 3) the application is a little bit smaller than on a device with 160 DPI, but that is not so much. The buttons would be big enough to press.
That is fine with fonts and graphics, but not with bitmap images and bitmap icons. For this images you have to use the MultiDPIBitmapSource
The runtimeDPI is set by the Flex runtime. In an iPhone application the default runtimeDPI is 160 DPI. To get the high resolution for the iPhone 4 you have to set the requestedDisplayResolution to true (in the application xml file). With that setting you get a runtimeDPI of 320 DPI.
On the moment (Flex 4.6) that does not works for the iPad 3 (the new iPad). You can display the runtimeDPI in your application and you will see, that Flex uses 160 DPI.
You can watch a good video about this here: