Google Accounts rolled out multimple sign-in features, "Now, you can visit google.com/accounts and click link next to "Multiple sign-in." Once signed into first account, you can sign-into two additional accounts from "accounts menu in upper right corner of Gmail." You can even open multiple Gmail tabs — one for each of your accounts," informs Google.
Watch out following things before using:
- Not all Google services support multiple sign-in yet. For services that don't support it (like Blogger and Picasa Web Albums), you'll be defaulted to first account you signed-in during a session. So if you click a link from Gmail to Blogger, you'll be logged into Blogger with "the first account you signed in with," even if you clicked the link to Blogger from second Gmail account.
- Google's working to make Gmail and Calendar work offline with multiple sign-in.
- Multiple sign-in only works on desktop, Gmail on ;phone's browser doesn't support this option yet.
- Since Google Apps customers can already sign-in to their accounts at the same time as their personal Google Accounts, this feature wont be added to Apps until the new infrastructure is in place.