DOF effect for Backdrops:
I've also found that DOF in Vue isn't worthwhile, when Photoshop gives good results much more efficiently.

Kind of hesitant to post, since I have not put much time or research into DOF (or checked out Chipp's tutorial yet) but:...
 
Rather than using the Z image, I put my backdrops into a separate Vue layer and do a multi-pass render to .PSD to get a Photoshop layer just for the backdrop, then do a "channel as selection" and erase the backdrop areas out of the foreground image layer. Then I Gaussian blur the backdrop layer.
 
With the backdrop in its own Vue layer, you can also hide it from renders and turn it off in your 3D viewports, which helps mightily to de-confuse your scene when your backdrop is a complex object.

Maybe not the best possible method, but it works well for me, so far.