By the way, one of the first 720p & 1080p Youtube videos, pretty awesome, isn't it? double-click to watch it in YouTube and you'll see the new HD resolutions.
Although it's still under development and you can only use them with the Dev channel version, I find them very promising! oh, and you can install, activate and use them without restarting the browser.
In my case I installed Google Wave, GMail, Facebook and Google Reader notifiers, and here's how you can do it: