The fact that Chrome OS will be entirely open source is great news because this should allow Ubuntu to take advantage of Google powerful software development team. Many Ubuntu developers, Cannonical in particular, are already helping to integrate Chrome browser into the Ubuntu desktop.
Could this mean the end of GNOME for Ubuntu? I am not sure on that one, but this may be something to watch. I am not entirely sure that introducing another windows management system is an entirely good thing for Linux either. There is already a lot of confusing out there among users between KDE, GNOME, Xfce, etc. But maybe the umbrella of development and backing backing of Linux by Google will help bring Chrome OS to the forefront. But, one of the great things that has always been true with Linux is that you have a choice, right?
Here is a link to the Google Chrome OS Announcement