Another way to solve this problem, and if you have Photoshop CS 6 Extended is to use the 3D features. I've provided ways to do this in the following a discussions:
Single layer with perspective and camera blur: Perspective manipulation
Multiple layers with stacking depth, perspective and camera blur: "Fake" 3d effect in Photoshop/Illustrator with raster images
This process is non-destructive and you will retain all of the resolution of the original image(s). However, it's harder to adjust the camera's Depth of Field falloff points in 3D than it is to use the Blur Gallery > Tilt Shift filter.
Cheers and good luck!