There is no smoking gun from Google yet, but we do have an invitation to see "a number of firsts" on Wednesday night, following the conclusion of the conference. The timing may be a bit odd, but there has been plenty of news around Samsung's upcoming Chrome Os notebook called Alex and it appears that Google is pretty much done with the Chrome start screen as well as a slightly changed Chrome OS UI that is more grey than blue. Of course, there is also the recently the launched file manager that is now part of Chrome OS.
It's a matter of your view whether Chrome OS is ready for the spotlight and commercial products. Our own tester, one of 65,000 CR-48 notebooks, suggests that Chrome OS is still a bit rough around the edges. For example, there is still no offline support for web applications. Google's I/O website suggests that Chrome OS will be a non-topic over the next two days as the company does not mention "Chrome OS" in its program at all. However, there are plenty of Chrome sessions that focus on building web applications as well as the use of HTML5 and apps is really what Google wants from developers. Personally, I would not be surprised if Google dropped the "OS" from the Chrome OS name and simply called the software now simply Chrome. For the user, it is difficult to make a decision between Chrome OS and Chrome anyway.
Your guess is as good as ours: Google may or may not announce Chrome OS, but there are not many opportunities to introduce the operating system and potentially give away free hardware to thousands of developers to provide an incentive to develop web apps.