If you are a subscriber to the Flash Media List then you will have seen Steve Wolkoff's announcement regarding the updated Flash Player 9 that's now available on Labs. The new Player not only adds support for Windows Vista, it also contains bug fixes as well as a new full screen feature.
Note we aren't just talking about full screen real estate within the browser here but actual full screen - without any chrome! Now that's a potential killer feature if you ask me.
There are however already some concerns that this feature could get abused - think Eyeblaster.

Owen has already blogged about this heavily and put up some sweet demos (before you leave a comment stating that it doesn't work: install the new Flash Player first).
I'm brewing my own little demo right now (which would be ready had Squeeze not crashed on me again) so watch this space.

Flash Player 9 Update
Emmy Huang's Blog
Owen's Blog

UPDATE
I've used an older clip to put together this little demo.