With the latest Chrome OS dev channel builds, Google has added a new about:flags setting called "Sign in with your Google Account."
But the flag does more than offer a visual refresh of the Chrome OS login screen, it's a complete redesign of the backend login progress. Google is in the process of deprecating the outdated and somewhat insecure ClientLogin API that the current login page uses. The new login page replaces ClientLogin on the backend with Gaia, the same login system that Google web services like Gmail, Docs and Google Plus use. Gaia is entirely web based so the new login screen actually opens up a stripped down minimal Chrome browser to display Gaia.
So what features do Gaia and the new login screen bring to Chrome OS? To begin with, Google's 2-Step Verification works.
Further, Google Apps users who are using SAML Single Sign-On (SSO) on their domain and don't know their Google password will be able to login to Chromebooks (they can't now).
But while Google continues to work on improving the new login screen, I don't recommend turning this on just yet. In testing the new login screen, some users have ended up locked out of their device and needing to do a stateful wipe in order to get things back to normal.
It's not clear if the new login screen will launch during Chrome OS 0.15's stabilization process or if we'll have to wait for 0.16+ but as we've seen in the past, Google is moving quick with Chrome OS updates so we shouldn't have to wait very long.