The rollout of Windows Live ID continues, this time with the new sign-in UI. From the Live ID blog:
Today we are rolling out a new sign-in experience for Windows Live sites like Live.com, Ideas, Mail, Expo, Favorites and Custom Domains. This is the next step in our Windows Live ID deployment.
There's much more still to come from the Live ID team, including multiple credential support. This has been provisioned already on the servers, you just need to install the Windows Live Sign-In assistant at the same time as installing a Messenger or Toolbar version that includes it. This will be available publicly in the upcoming Messenger beta refresh Brandon mentioned earlier in the week.
Multiple credential screenshots (Click to enlarge):