Google Tests Multiple Accounts Sign in
Friday, July 16, 2010 6:34If you use several Google accounts on a daily basis, you would probably like to be logged in to all of them at the same time. You have to use several different browsers to achieve that currently.
Now, according to Google Operating System, Google is testing a feature that will let users log in to multiple Google accounts in the same web browser. Personally, I have at least four different Gmail accounts open at all times, and this feature is very high on my wish list.
Google services that are currently being tested include Gmail, Reader, Sites, Calendar, Code and Docs. There is one limitation: if you turn on multiple sign-in, you cannot access Gmail in offline mode.

Multiple sign-in will let you open Gmail in multiple tabs, log in using different accounts and read the messages from all your accounts without opening another browser. Right now, you have to log out before logging in to a different account.