This question has been asked more and more as time goes on. Do Adobe AIR or Flash apps utilize multiple cores or multithreading? So here is the official answer:
NO (as of May 2012).
(Multi-core or multi CPU processing is more accurately described as multithreading. A thread is a set of code that runs line by line. A CPU core can only execute 1 thread at a given point in time (unless it has hyperthreading - 2 threads at a time). A computer with 4 CPU's and 4 cores each CPU can run 16 threads at any given point in time. If a device only has one core than all running threads have to share that one core.)
Both AIR and Flash are the same platform, and process code identically. If Flash implemented multithreading than so would AIR. The only difference between AIR and Flash are features.
There are 2 exceptions to this:
As of AIR 2.6 images loaded using Loader can be set to be decoded on a separate thread.
As of AIR 3.2, Flash 11.2, Video is finally decoded on a separate thread. And depending on some factors and requirements, that separate thread that is handling the video data acts simply as a forwarder and forwards the video data to the GPU where the GPU distributes the decoding across its many cores.
Adobe plans to implement multithreading into the AIR and Flash runtimes the second half of 2012.