Just switched the machine to boot from HDD to USB and it worked flawlessly. I wound up doing this because I bought some KWINN drive trays for my two 5.25 bays. Although I'm only using ancient 250GB ATA-133 drives, I feel it a necessity to be able to upgrade quickly and also have the ability to pull a drive and run if an emergency arose. I've been using digital cameras and camcorders since 1998 so 10+ years of memories means a whole lot to me even if it's only 100GB of data.
All in all an amazing solution using an IBM ThinkCentre I purchased on Ebay for $54
The only problem I noticed was that the Mirroring of these two drives would occasionally fail with a kernel panic when the NASLite OS was on Disk-0. Now that the OS is on the USB drive (Disk-3) I can safely mirror Disk-0 on to Disk-1 without a problem.