I posted a new article over at TipSquirrel.com on the rarely used Lens Blur command.
Selectively blurring an image can help your viewer find a focal point. Photoshop offers a realistic lens blur that also produces depth-of-field blurring. This allows some objects to remain in focus while others fall gently out of focus.
You can be very specific in regard to the blurring if you make an accurate alpha channel to serve as a depth matte. The depth matte defines how far away things are from the camera.
Read the whole article here – http://www.tipsquirrel.com/index.php/2010/10/adding-lens-blur-in-photoshop/