I was noticing a yellow box appeared always on my GApps accounts but always ignored. Today I read it and found that Google is transiting, this fall, all of the Google Apps accounts to new infrastructure where they will actually can act exactly like Google Account. And can access even more of the Google Services with that account. But till the automated procedure of upgrading all of the accounts, Google is actually giving you opportunity to do it your self with any or all of your Domain users.
While looking through it I just found that Google has also started Multiple Signin. That you can signin to multiple Google Accounts at the same in the same browser without signing out the other. In this new interface it gives the option to turn on/off the Multiple Sessions feature on your choice. Additionally this feature would also be available to the users on the Google Apps accounts which have been transitioned.
To turn on/off the feature, After signing in, go to your Google Accounts page by clicking the link "My Account" and look for the option "Multiple sign-in" to check and edit.
or alternatively, after signing in to any of your Google Account, go to following URL to turn on/off the Multiple Sessions feature
Google Multiple sign-in feature is just different than the Windows Live Linked Accounts. I am not sure exactly about the date or year but Windows Live has provided Linked Accounts feature a far before. I have been using it since more than 2 years. Unlike the Windows Live Linked Accounts, Google Multiple sign-in doesn't link permanently two or more accounts. You just use it temporarily to help yourself not signing out from other accounts while as Windows Live - Linked Accounts actually permanently link two or more live accounts that you can switch from first to second any time.
Do you think it's helpful for you?