The Google Operating System blog and CNET announce that Google will be rolling out a multi-account sign-in functionality. Rather than users having to login to different Google accounts individually, this new system would allow users a single account sign on for different Google accounts. The functionality will support up to three accounts. A simple drop down menu will allow users to switch from one account to another easily.
Once rolled out, users will need to opt in to the service from the user's Google account management page. The single sign on feature will work in Gmail, Calendar, Reader, Code, and Google's Sites.
This solution however does not allow users to be signed in to two or more accounts at the same time. It is simply a quick switch functionality.