RST version 10.1.0.1008
BIOS versions A07, A10, and A11
Dell HDD P/N: VV4P8
Drive Make / Model: Seagate ST250L0007-9ZV14C
I should have also mentioned that in addition to powering off the system, I've been able to resore the drive performance back to normal by putting the PC into Sleep mode and then waking it up and also by making a BIOS setting change. (In my case, I enabled SMART reporting, but I suspect any change would have had the same effect.)
When the issue is occuring for us, all of the performance metrics within Windows 7 look good except for the Drive Response Time. Typically, we see Disk Response times of 10 to 15 ms when starting an app such as IE or Word. However, when the drive is in this state, we're seeing response times that are anywhere between 1,500 to 20,000 ms.