One method I like to use is the Replace Color adjustment. Make a new layer first, and then go to Image - Adjustments - Replace Color. Make sure the localized color clusters box is checked (CS4), and then slide the fuzziness slider all the way to the left. Click on the background and then hold the shift key while dragging the cursor through the area you want to affect, watching the display in the Replace Color box as you go. Don't go too far, you want to add the last bit with the fuzziness slider to make the edges of your selection smoother. Then go to the saturation slider and set it at -100 and up the lightness to where you need it . If you did select a bit of the subject, you can cover that up later with a black brush on a layer mask. It's pretty fast and easy and does a nice job one you've gotten used to it.