For large datacenters, DC can be a big improvement. http://gigaom.com/2012/01/13/the-next-big-thing-for-data-cen... But this is mainly where UPSes are involved, or solar power. That might not be relevant to a house, but it could have other advantages besides efficiency. Imagine all your computers had tiny DC-DC converters instead of heavy, hot bricks of inverters. Laptops would only need a cable to charge instead of a power brick.