I just got my U3 yesterday. I spent some time attempting to set it up on a Win7 x64 machine at work, but ended up having Zombie issues nonstop. I brought it home and set it up with my Win7 x64 VM on my rMBP and it ran beautifully using the 4.6.1 cgminer from BITMAIN and Zadig. I am making the assumption that it is a driver or timing problem and will investigate further from here.

I am currently using --bmsc-voltage 0850 and --bmsc-freq 0982 and achieving 42gh/s using the stock power supply. The U3 is also drawing only 44 watts at the wall with these settings.