After using FreeNAS for about one year, I'm pleased with the results. Its working great for me, and so I'm going to continue using it, and will likely use it more in the near future.
Since I wanted to test FreeNAS, I setup a local mirror of some debian repositories that I could use for machines on the same local network. Its been working fine for the entire time! The storage medium I was using was two 250GB hard drives, setup as a RAID1 device. I ran into a problem with one of the disks, probably due to a power failure which occurred recently, but I rebuilt the RAID and it completed successfully.
Check out the post I wrote when I first setup the FreeNAS server: