Check this out. Odd name but great concept:

The linear LED is hidden within the plasterboard and is invisible until activated.  I can see us using this for a variety of applications.  Their main market seems to be commercial but we are already working on including it in a current domestic lighting design.   http://www.vcut.co.uk/index.php/silent-light.html

They also make superb custom plasterboard lighting coves: