Oops, deleted post just as you were replying.
As said, we're building this:
http://blog.backblaze.com/2011/07/20/petabytes-on-a-budget-v2-0revealing-more-secrets/
We've got 210 staff members generating a shitload of data (medical research, imaging, etc), so the bigger, the better. We're building one to start with, then possibly another two.
Just checked UMart; getting a quote off them now, they seem to have stock.