Yes, quite allot actually as I do storage for a living.
First off raid6 failures protect against hard drives that were all made at the same time and installed. This is true if your bought the array, as an array, from a vendor. But if you made it yourself from multiple disks the changes of parallel failure is negligible. And as far as raid6 goes I spend a considerable amount of time converting 6+2 raid 6 arrays into 7+1 raid 5 arrays. In these cases 12TB would be very small.
I also have my own disk arrays at home. Less for enterprise storage and more for those HD ATSC recordings my myth box makes. In it is a 4TB 5x1TB SATA array with a hardware raid card (really it is driver assisted). Aside from the slow write performance (it is expected with raid5) they run fine.
Reading the posting I wonder to myself if he has every watched a raid array rebuild. For that matter has even watched a SAN attached array work. Yes it takes time to rebuild (depends on the size of the disk). But other then slow access time that array when it is rebuilding it is rather transparent to the hosts using the array (not to mention it is pretty hard to saturate and enterprise raid array).
Why someone would mirror a set of mirrors (1+1 or 11) is beyond my understanding. Many of my customers use raid 1+0 (for speed). I have even seen customers use raid 5+1, but we tend to call that "paranoid raid".