This afternoon we launched the Flash Player 9 Update public beta on Adobe Labs. The Update includes bug fixes, support for Windows Vista, and one cool new feature: full-screen mode in the web players.
Flash Player 9 Update technology page
Flash Player 9 Update download page
Full-Screen Mode wiki article

Hi!
To all lazy Flash developpers : if you want to see what the fullscreen feature looks like, you'll find a link to a demo on that page : http://daspblog.canalblog.com/archives/2006/10/05/2836593.html
Have a nice day!