Here’s Colin Smith on the new Camera Lens Blur effect in CS 5.5:
“This new effect gives you the ability to create the optical effect of a real camera lens blur. If you need to add depth to a scene, or obscure something in the frame, Camera Lens Blur will do that and make it look completely realistic. You also have complete control parameters like iris shape, blur maps, super whites, gain and threshold.”
Chris Meyer has more on this feature in his complete training series at Adobe TV, AE CS 5.5: New Creative Techniques Introduction.