This is a surprisingly easy effect that gives the impression that the subjects in the photo are popping out (okay, in this case, walking out) of the photo. This popular effect is probably used the most in print advertising campaigns, but now I'm starting to see everyone from wedding photographers to children's studio photographers use the same technique, because it adds 3D depth to a 2D image.
Quick Tip: Paint tools have Blend Modes too
You're probably familiar with layer Blend Modes, where you change how a layer interacts with the layers beneath it. In Normal mode, it doesn't interact; it just covers whatever's beneath it. Well, Photoshop's paint tools have the same feature, and choosing any Blend Mode (other than Normal) ...