1. double click your image in the layer palette to make it layer 0 instead of a background layer
2. apply a layer mask.
3. fill the layer mask with black
4. draw a hard edged white circle/ellipse/rectangle/whatever.
5. apply a gaussian blur to it
6. create a new layer underneath this layer and fill it with whatever background color you like.
1) Create an Overlay layer above your image filled with neutral gray.
2) Draw an oval around the subject.
3) Feather by something like 150 pixels.
4) Use levels and drag the left slider to the right to "darken to taste".
It's pretty quick. And being in an adjustment layer, you can turn it off or on, or even change it pretty quick.
