The new updated beta Flash Player 9.3 (currently available on Adobe Labs) will support a full-screen mode which will allow sites to display full-screen Flash content over the web.
According to this blog post by Emmy Huang from Adobe, there are a few security restrictions that developers need to be aware of, but none of them seem to be anything that is a cause for concern. And, one of those "features" I actually like -- when the user first chooses to switch to full-screen mode, the player will display instructions on how to leave full-screen mode and then fade them out after a few seconds.
I really see sites like YouTube and others with heavy video usage standing to gain the most from this new feature, but I'm excited to give it a go.
More information here: