While Flash Builder v4.5 was supposed to be the version that added mobile support for developers to go cross platform it only really supported Android at first. From what I am hearing from devs this new Flash Builder v4.5.1 along with Flex 4.5.1 allows you to follow the similar export process to develop apps for the PlayBook along with Android and iOS devices from one codebase. I am waiting to hear back from Adobe on exactly what is different between v4.5 and v4.5.1 but you can check out for yourself.
You can find out more about the update and download it from Adobe. Thanks to Ashley for the tip via Press Release