Cranshaw mentions "tens of hours of downtime" as a drawback. Given that downtime sometime corresponds with times of high load aka, the really important times, that's going to be a deal killer for most.
But his architecture does seem to be consistent with a "minutes of downtime" model. He's using AWS, and has his database on a separate EBS volume with a sane backup strategy. So he's not manually fixing servers, and has reasonable migration routes for most disaster scenarios.
Except for PBKAC, which is what really kills most servers. And HA servers are more vulnerable to that, since they're more complicated.
But his architecture does seem to be consistent with a "minutes of downtime" model. He's using AWS, and has his database on a separate EBS volume with a sane backup strategy. So he's not manually fixing servers, and has reasonable migration routes for most disaster scenarios.
Except for PBKAC, which is what really kills most servers. And HA servers are more vulnerable to that, since they're more complicated.