Anyone who has pre-ordered Left 4 Dead 2 through Steam can now start the pre-loading process. Weighing in at a little over 6GB in size, it's a good idea to start your download early so you can be sure to have it ready when it's unlocked on November 17th. Steam won't prompt you to start the process, so right click the title in your client and under "View pre-load info" you can start it manually.
While Valve hasn't revealed just how many people have snapped up Left 4 Dead 2, you can expect there will be a substantial load on the game and download servers at launch. There is also an unclear status on how the game will fare worldwide, especially in regions like Australia where it's still technically banned (though the censored version will apparently make it in).