Comment from Larry Osterman's weblog:
"you can't speed up hard disk copies by throwing more threads or overlapped I/O at the problem, because file copy speed is ultimately limited by the physical speed of the underlying media - and with only one spindle, it can only read or write to the drive one operation at a time."
I thought with RAID, byte striping, SAN and the like you can't really assume what your underlying physical reality is anymore. I once heard this from a technical staff of a high-end RAID provider: "that anything you can throw into the SCSI bus, their RAID box will be able to write". Not really sure if it were true but their disks are really fast.