Bit overkill?
Even with the current limit of 21 drives, you can climb up to about 40TB of usable raw space with today's technology. That's a whole heap of space.
With 3TB drives coming down the pipeline in 2011, and looking like unRAID 5.1 supporting these drives (as long as current crop of motherboards support them), we could potentially see 60TB raw space..
I've only got about 7.5 so far.