FreeNAS has been my fav. workgroup server solution for awhile. Flexible, price is right. Performance isn't the best, but it's been fast enough where I've deployed it. I have quite a few of them out there. Can't remember the last time I've had to do any real maintenance on them. Sadly, I find FreeNAS shares via Samba (Windows Sharing) better than Windows does. One of those "just works" solutions, despite not being as fast as some of the other NAS solutions out there. Then again some of mine are running on PII-400MHz computers.
I definitely understand the high gig requirements. I have 8 TB of internal drives on my FreeNAS. It gets used as a server and once a month it does a differential backup to a FreeNAS box at one of my data centers. Every so often I'll manually carry a few 1TB ESATA drives between the two machines and do full backups of a few drives at a time.