Greg Owen posted a nice follow up on the EffectiveUI blog.

We worked with Adobe to see if we could work on something to help alleviate this issue, but even with a custom UIMovieCip Class Adobe provided, we still saw large CPU hit.

So, again, at this point, for larger applications, it is probably best to stick with stateless skins if you are going the graphical approach.

Read more on the post here:
EffectiveUI Blog