I see that there is still a lively debate concerning our choice of user interface (UI) toolkit for Flash Player 9. To review, we selected GTK, mostly because the Player 7 codebase we started with already implemented a bunch of stuff with GTK.
Everyone has their own favorite toolkit. I just wanted to write this post to advise people not to get too hung up on this UI issue because Flash keeps its interaction with system UI toolkits to an absolute minimum. In fact, I am authorized to post a screenshot showcasing one of the major uses the Player has for a UI toolkit (click for full context, including Firefox browser window which depicts a small SWF from our vast internal testing suite that isolates Flash's file upload muscle).