The thing that helps with the magic of this picture is the movement, which is achieved by actively moving the camera whilst the shutter is open. I have talked about this before and so won't go back too much over the theory behind it except to point out that I normally don't like flash and blur images where there are no points of light to give that blur. Evenly lit scenes are normally very difficult to make good blur from and it only worked in this case because the author's face was slightly in shadow and because the available light exposure is still over one stop underexposed at 1/8th of a second at f5.6 on ISO 100.
The flash and blur picture above as shot on a Canon EOS1D MkII with a Canon 16-35 f2.8L lens. The flash used was a Canon 550ex triggered with a Pocket Wizard. For the record, the image on the left was shot on the same model of camera with a 24-70 f2.8L lens. It was shot at ISO200 using a Canon 550ex flash with a Sto-fen off to the right of the camera about two metres away and there were white walls and a white ceiling to reflect plenty of light back to make the lighting reasonably soft and quite flattering.