Apparently a lot (most?) SATA drives are actually configured so that you can't use more than one in a system...even though the motherboard may have LOTS of connectors for them.  The problem is that once you plug in a couple of SATA devices, they interfere with each other.  This leads to TERRIBLE corruption of any new data (like say...copies from one drive to another).  I'd suggest anyone with more than one SATA drive first test by copying a fairly large file from one drive to the other and then compare the two files (you can just open a command prompt and type COMP and tell it the location/name of each file).  If it's corrupt you probably need to enable SSC (Spread Spectrum Clocking).  I had been trying to figure out what the hell was causing this issue on my machines and finally noticed an inadequately documented jumper ("SSC enable").  I did a little digging and it turned out that's what the jumper is there to fix.

Since I had the problem on 4 different drives from 4 different manufacturers with 3 different motherboards (About 5 years old to just recently released) I would say there's a good chance this will affect quite a few people.  Yet another thing nobody ever seems to tell you...not unlike the FDISK /MBR thing to fix the boot sector after having installed linux. (Something I'm guessing microsoft continues to ignore in the hopes that it will give linux bad press)