In System Profiler on my 2012 MBA, I see four entries in USB: 3 "USB High-Speed Bus" and one "USB SuperSpeed Bus." When I plug in my iPhone, it appears under a "Hub" entry in the same "High-Speed" bus that has the keyboard and bluetooth controller. When I plug in my USB 3.0 hard drive, it appears under the SuperSpeed Bus no matter which port I plug it into. So the SuperSpeed Bus must be for actual USB 3.0 devices, and since there is only one "SuperSpeed Bus" and no "Hub" in it, my question is: can the 2012 MacBook Air support two USB 3.0-speed devices, or will one always run at 2.0 speeds? EDIT: Maybe someone who owns two USB 3.0 hard drives could test this?