This made my Sunday: although it’s been official for almost a month, I’m just now learning that Google now supports logging in to multiple accounts simultaneously.
Now, you can visit google.com/accounts and click the link next to “Multiple sign-in.” After you sign into your first account, you can sign in with up to two additional accounts from the new accounts menu in the upper right hand corner of Gmail, then easily toggle back and forth between them. You can even open multiple Gmail tabs — one for each of your accounts.
If you’re a Google Apps customer you may have noticed that this has always been allowed so I can’t say that this is a huge surprise — though I’m quite happy to see they’ve taken the steps to improve the usability in standard google accounts by adding a menu next to your account name. According to the post, the drop-down (for something similar) will be coming to Apps customers after they roll out their new infrastructure.
Since Google Apps customers can already sign in to their accounts at the same time as their personal Google Accounts, we won’t be adding this new feature to Google Apps until the new infrastructure is in place.
via Access two Gmail accounts at once in the same browser – Official Gmail Blog.