I have literally been seeing these for years, but i am not sure how prevalent they are in new buildings or houses...i would think that as long as USB is the way smaller electronics get powered these would be a big hit.
The only thing that i kind of worry about would be if you (or a kiddo in the house) plugs in something with a USB 'male' into a dedicated USB 'female' power jack...like my headphones or a mouse...what would happen? Ideally, nothing, but i could see the 'appliance' getting fried or worse the appliance and the person who plugged it in getting fried.