If you asked “what will a GoogleOS look like?” – most people would answer that it’ll be an AJAX-powered copy of the Windows desktop. In other words, a WebOS (aka webtop). To remind you of what a WebOS is, it is basically a virtual desktop on the web and has various built-in applications.
There are many ideas thrown around here, and most of them make sense. Since Google is releasing many web apps that mimic desktop apps, it almost seems like a natural progression to make an OS. They would have to deliver something explosive in order to steal people from the competition though.