I'm not using iPhoto myself, so I cannot help you with any specifics (I use GraphicConverter instead).
But the basic communication with the camera is done by a Mac OS
X framework anyway.
Macs generally don't care about which ports you connect a device to or whether you alternate between different ports.
That said, some USB hubs may cause problems with data communication. That particularly affects USB hubs without their own power supply, sometimes including Apple's older keyboards (the new aluminium keyboard has fully powered ports).
USB cables can indeed be a source of troubles, though, particularly cheap ones.
If it's an intermittent problem, it may indeed point to a shoddy cable, particularly when a different camera with a different cable works reliably. Testing the cable would require using it with a different device than your camera. You'd have to check if you've got any matching ones.