Recently I came across a video on Youtube, which shows technology of the Smart Window.
The Smart Window casts a touch-controlled interface onto transparent glass with ambient light. Samsung was demonstrating a whole range of applications from Twitter to Microsoft Office, all touch-controlled and viewable directly on the glass. Images are viewable in daylight, and there's a nighttime mode that uses side-lighting and flipped colors. It could be found in hundreds of movies and TV series, starting from the Star Trek.
It seems that you only have to solve the problem of voice recognition, and the touch screen will be exactly the same as in the Star Trek.
Can you imagine putting one of these in every room of your house?