I have found something very interesting.
I have 2 F16 machines, pretty much set up identical except one is running 64 bit, the ohter is running 32 bit PAE kernels.
Using the very same 2TB external hard drive, both machines have USB 2.0 ports which the drive was plugged into for this test.
On the 64 bit machine, My transfers were around 39MB/sec over a 500GB transfer. (Fresh drive, nothing else on it.)
Delete those files off the drive, plug it into the 32 bit machine. (checked to make sure the same mounting options were being used). The transfer dropped to around 5MB/sec on the same file transfer.
Source drives were identical WD Caviar black drives, both get about a 128MB/sec sustained transfer rate, so the source drive isn't the issue.
While I could see a small difference in transfer rates, this is a HUGE difference. (about a 35MB/sec difference) and yes, I did make certain that the USB port and drive were seen as USB 2.0 and not 1.1