Google has made it less painful for people with more than one Google/Gmail sign-in to move between accounts. Now, rather than run multiple browser windows or use tricky Firefox techniques, multi-account users can toggle between their accounts in Gmail and other apps.
It's very early-stage stuff, and Google's making that very clear. The multi-account switching, which we've seen in previous screenshots, only works at the moment in the Calendar, Code, Gmail, Reader and Sites apps. And when you go to activate it, at your google.com/accounts page, you'll need to check off four different boxes to indicate you understand just how alpha-level this feature is.
Note, too, that this is not an easy way to switch between Gmail and Google Apps accounts — that's coming, but you can already sign in to multiple GApps accounts at the moment. Does multi-Gmail sign-in work as expected for you? What other apps would you consider account switching crucial for?
Access two Gmail accounts at once in the same browser [Official Gmail Blog]