Personally I find the Gmail UI to be unusable for serious work. The threading is awful (based on subject instead of headers and collapses everything into a linear sequence) quickly going through an inbox is painful because the split view is incredibly basic and the way it tracks read-status in threads is far too unreliable to find what you need to see. Plus every time you open a long thread you need to scroll forever to get to the new messages. It makes me understand why most of my coworkers don't read their email.