I have two 500GB Momentus XT drives in my i7 MBP. each filled to 60-80% capacity. But when I'm doing anything from typing to playing back HD video in FCP, it lags and stutters, then catch up to itself. I did the firmware upgrades to the hard drives, and I have 6GB of RAM. What on EARTH would be causing this? It's driving me crazy! I ordered a Hitachi standard 7200RPM drive to swap into this to see if it's a hard drive issue or a RAM issues, but I'm guessing it's the Momentus.