I seldom have luck using the pen tool (I need more practice). Regardless of the selection method, it seems like I always have to touch up the mask edges, so I usually just paint it free hand to begin with. Using the \ overlay as a guide, this method goes pretty quickly.

I created the background with the Render Clouds filter, using two colors from the real background. Using similar colors to those around the subject sometimes makes the masking easier to blend the layers.

Added a Render Lighting filter to spotlight the background and a little color correction for skin tone with a Curves adjustment layer.

Frame just to simulate a finished look.

I didn't do this, but skin tones might have benefited by Assigning Colormatch profile, then Converting to desired output profile. This seems to work well per Photoshop Mama's tutorial recommendation.
forum discussion: http://forums.dpreview.com/forums/read.asp?forum=1006&message=26440101
original image by Lew (S601superflow):