Just to let you know that I have successfully reprogrammed my QCX a couple of times with a USBTiny ISP with the power for both the programmer and QCX both coming from the USB port of my laptop. My programmer has a configuration jumper to allow separating the power but I left it on.
Warren,
I just checked, my USBasp tells the PC 50mA (USB View) so if the PC really limits power on the USB outlets then that's why mine does not work.
I guess they are not all equal.
73 Alan G4ZFQ