My custom scripts used to root the Chrome OS that comes on chromebook machines, with some extra goodies, enjoy. My normal choices for firmware are 1,n and then 6,y followed by a reboot. This also comes with a nice 4Mb hosts file to help block out some of those annoying ads that we all despise.
WARNING!
THIS SCRIPT DOES REMOVE THE ANDROID APPS ABILITY ON YOUR CHROMEBOOK! If you wish to keep Android apps, I suggest you comment out lines 12-17 in the cros/fst/root file.