Kent Trammell published few days ago an interesting article about using PBR (Physically-Based Rendering) in real time directly in the Blender viewport.

Even if it is not a real PBR render the final result is quite the same using some of the new features of the Blender 2.75 version.

For more information read the full article here: https://cgcookie.com/blender/2015/05/20/pbr-in-blenders-viewport/