It has taken a while for the economical advantage of this to trickle into user space. Electronic devices are almost all DC in nature, and the efficiency improvements here are not actually the computers, they are the lack of individual power supplies. Other poster have made comments about laptops, but normal laptops are actually no more efficient than desktops. They use less power, but that power brick is not any more efficient than a good desktop power supply.
What they get to do here is run one big, presumably very efficient power supply, and run it outside of populated space, moving the noise and heat generation to where it can be more efficiently controlled.
Of course telco types will say "Umm, yeah?" because a lot of telco heavy iron has been DC forever, for the same reasons TFA is bragging up this system.
This doesn't apply very well to consumerland, because houses don't lend themselves well to special DC wiring that doesn't easily move when you rearrange the room.
And before people start asking "Why don't the power companies just use DC?" Electricity transmission over distance is much more efficient as a high voltage/low current AC than DC current, especially since you can't use transformers on DC.
But I can very easily imagine datacenters utilizing a rack sized high efficiency DC power supply to run row(s) of server racks. This would tie in very nicely to Googles battery-in-every-server method.