Monitoring The USB Bus

If you install the XCode developer tools (http://developer.apple.com/) there is a USB Prober application under /Developer/Applications. You *might* be able to extract that kind of information, but I doubt it will be easy to figure out per-file basis.

I think what you want is to use the rsync command with --stats option.
> rsync --stats src dest
By default, it will act like standard cp command.

Check out the Disk Activity tab in Activity Monitor. You can't separate it by device, but if you make sure that the big file copy (or write) is the only major disk operation going you'll get a pretty good approximation.