Original image (without the drop shadow layer effect) created following this tutorial on YouTube: http://www.youtube.com/watch?v=YIbjIsWpSV8&feature=relmfu
After completing the steps in the tutorial, I selected the image and copied it to the clipboard and pasted it on a new layer, then went to Layer/Layer Style/Drop Shadow.
Fun technique - if you want to try it, don't forget to click on new for the adjustment brush in Camera Raw, each time you change the parameters.