Google Desktop is leaving beta today. Along with this news comes a new feature that we call "Quick Search Box". To use this feature, simply hit the control key twice and you will be presented with a search box in the center of your screen.
The Quick Search Box located in the center of your desktop enables you to search the web and your local computer as quickly as possible. You can simply press Ctrl twice to call up this search box at any time, and press Ctrl twice again to hide it. If you don’t want to use the Quick Search Box at all, you can disable it on the Google Desktop preferences page.
This is a great feature that I'm sure I will be using quite often.