Flash Player engineering manager Paul Betlem, as relayed by John Mack:
First and foremost, Flash Player 10.1 is a full-fledged Cocoa app (though legacy Carbon support remains for some browsers that require it). We now leverage Cocoa events, use Cocoa UI for our dialogs, leverage Core Audio for sound, Core Graphics for printing support, and use Core Foundation for bundle-style text.
I'm happy for you, Adobe, and imma let you finish. But Creative Suite 5 was also written in Cocoa, and even though it uses the same Apple frameworks I'd hardly call that a successful Mac-native UI.
Still, Flash Player has been one of the least Mac-like apps in common use, so any progress is good progress.