Half-Life 2 pre-loading begins to Steam account holders today. Over the coming days, those who have selected the pre-loading option will have encrypted Half-Life 2 files delivered to their PC. No purchase is required to pre-load HL2, but is required to activate the game. Purchase options will be released soon. Then, the moment the game is made available, those who have pre-loaded and purchased Half-Life 2 via Steam will be authenticated and ready to start playing. For more information, please visit steampowered.com.
This of course makes for a bold statement that the game is pretty much done. If you are one of those who won't want to wait for the game to become available in store shelves, you will appreciate the alternative Steam gives you.