The combination ALT + SPACE pops up Launchy. You type some characters that are in the application name, for example "studio" for Visual Studio 2005. Press ENTER to accept your choice. Sometimes there are more options available, you can browse those using the UP and DOWN keys.
Besides this basic launching there are some enhanced actions available. For example type "Google" press the TAB key and type your search words. And the Google webpage pops up in your default Internet Browser with the search query you entered.
Read also the other productivity enhancements: