Google introduced "tabs" to their email experience last May. After over a year of data collection, it seems the jury is still out as to whether or not the tab configuration dramatically helps or hurts promotional emails and newsletters sent by marketers. However, here is a bit of research and a debate as to whether or not the tab formula has a significant impact on open rate.
While email open rates are down since the intro of tabs MOST email opens occur on iOS devices that do not display email in tabs (followed by Android device access - see graphic above). Where does this leave us? Tabs might not be so bad after all, and with apps like Unroll.Me and more cropping-up people are getting even better at organizing and sorting email content that isn't coming directly from another contact and it seems tabs might not be the "make or break" factor.