I wonder about the single point of failure posed by the power supplies. One failed box is not a big deal (since I assume the data is replicated over several). But, what if they get a bad batch of supplies and see a relatively high failure rate? I wonder how high a power supply failure rate they can handle.

The need to stagger the power on of the two supplies poses a problem. What if power to a data center is lost? When power is restored, all box will try to start, blowing all fuses. Granted, this is a catastrophic event, so its frequency should be very low. But, this also seems like an area that could be automated.