After running it about 20 hours I have nothing to complain about the U3 so far. I will keep it underclocked because it seems to run quite stable that way. And it doesn't matter anyway 50 Gh/s or 67 Gh/s is way too little in any case these days.
Where did you pick up a U3? I'm looking around... I'd like to pay bitcoin.
I got mine from
www.usbminer.ch and I also paid with Bitcoins.
And regarding the issues so many owners of the U3 have, no worries my U3 isn't flawless either. My U3 did zombie after running it for about 24 hours. I had to replug the USB-cable to bring it back to life. No overheating issues so far but then I do underclock and undervolt it.